Geology & GeoMetallurgy

Geology & GeoMetallurgy 2017-04-04T06:58:01+00:00
  • To participate in the 911Metallurgist Forums, be sure to JOINLOGIN
  • Use Add New Topic to ask a New Question/Discussion about Geology and Geometallurgy.
  • OR Select a Topic that Interests you.
  • Use Add Reply = to Reply/Participate in a Topic/Discussion (most frequent).
    Using Add Reply allows you to Attach Images or PDF files and provide a more complete input.
  • Use Add Comment = to comment on someone else’s Reply in an already active Topic/Discussion.

Geophysical method to explore Primary gold (51 replies and 2 comments)

Maya Rothman
2 years ago
Maya Rothman 2 years ago

In Gold Exploration, what is best Geophysical methodology or technique to explore primary gold, and establish quartz veins in Mica Schist bedrock.  Our exploration license is producing Gold Nuggets at 30 cm depth using metal detector. I know I can either search for the primary gold or the quartz host rock.

JohnnyD
2 years ago
JohnnyD 2 years ago

I assume you are referring to a standard type of metal detector as used by prospectors. I don't know your geology but 30cm depth would probably be the limit. Gold is mobile in humic acids and thus any nuggets in soil may not represent the top of the gold-bearing reef. What do the nuggets look like?

If you are looking for quartz reef gold then you are looking for structurally controlled features as likely as not. These need mapping at the surface, if you have exposure. If not, then you need a geophysical method that will distinguish the gold-hosting structures from the bedrock; I would start by digging costeans across the likely structures to see if they are there, as this would be cheapest. You might also get lucky if you use IP. It might pick up water in water-filled fractures following the reefs; it might pick up a conductive system of say, pyrite, related to the gold-bearing reefs; it might show that the quartz reefs are less conductive than the country rock and thus allow mapping them geophysically.

However, you cannot beat surface mapping, structural geological analysis and drilling. Also check for gold in pyrite/arsenopyrite if you have those, and analyze for tellurium as you go as this might be an indicator for calaverite.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Resistivity and IP will provide substantial depth penetration and can be combined with surface geology and drilling results. Begin with a small area and expand as the method(s) prove themselves.

Low-frequency GPR. Only the low-frequency electric profiling with GPR. Measurements 25-50-100 cm, the real depth of 170 m.

I believe there is no geophysical method that can delineate gold directly, I am talking of gold contents varying say 5 to 10 ppm on average, unless your target has gold in percentages and fractions.
If you have sulphide and /or magnetite dissemination associated with the load or the reef is highly fractured, SP, Resistivity, EM & IP could help in delineating target zones provided the geophysical surveys have sufficient resolution and you have good geological control for interpretations.

Helena Russell
2 years ago
Helena Russell 2 years ago

Ground Magnetic survey is the best for searching a gold deposit, because most sulfides associated with magnetite and these sulfides carrying Gold.

And see Goldberg I.S. et al. Mobile Forms of Elements: Their Use im Geochemical Mapping and Exploration (Google)

My personal experience with metal gold in quartz reeves, having pyrite-chalcopyrite-Arsenopyrite also with it, searched out by ground geophysics, SP and IP in parts but without sulphides, never could succ.eed in geophysical prospecting. Pyrrhotite-magnetite, extremely rare, may respond with magnetic survey across the strike, though anomaliesshow could be too lean.

JohnnyD
2 years ago
JohnnyD 2 years ago

One problem with the initial issue raised is that all we know of the geology is that it consists of nuggety ground above mica schist. The gold could be coming out of non-economic quartz "sweats" in the mica schist and the nuggets could be a secondary accumulation in the top 30cm, here presumed soil. Attempting to carry out any type of geophysical survey without first understanding the source of the gold is a complete waste of money. Assuming poor exposure the best approach is to dig some deep costeans, say 2m deep, to try to understand the source of the gold and when sampling and analysing consider that any gold values might be due to supergene enrichment. If the costeans reveal reasonable quartz reefs/veins carrying gold, then the next step is to use the data to develop a better idea of what is controlling the reefs, and perhaps bring in an inexpensive man-portable rig to test some of the reefs/veins maybe down to 20-30m to obtain core which can then be tested to determine if one actually has rock with measurably different geophysical characteristics so that one might have a chance to assess the best geophysical method to be used in exploration of the system. As the rocks are mica schist, they could well carry secondary "metamorphic" magnetite and pyrrhotite which would give completely misleading geophysical signals.

First, understand the rocks. Only then consider spending money on geophysics.

Helena Russell
2 years ago
Helena Russell 2 years ago

You may find this application note of interest: Identification of Lithology & Base Metal Anomalies – Pathfinders for Gold Exploration Using Portable XRF Analyzers
Since gold exploration is in discussion, Marlene from Thermo Fisher Scientific suggests of link up with pathfinder elemental analysis, which is easy and straight forward. geophysical and many geochemical methods of Au exploration have advanced enormously in the last decade.Some common geophysical methods that are used to map hydrothermal alteration zones include airborne gravity, 3D modeling of electrical data,and infrared spectroscopy (satellite, airborne, andfield-based). Although these geophysical methods are very crucial for gold exploration, geochemical methods – including portable x-ray florescence(XRF) – remain as the only methods that can measure concentration of gold and other associated elements.

Gold is mined as a primary product or as a by-product from a wide range of deposits. Its deposits are classified into three major classes:

  • Orogenic vein-type deposits formed during orogenic events,
  • Reduced intrusion-related Au-Bi-Te-As mineralization in post-orogenic granitic intrusions,
  • Oxidized intrusion-related deposits (porphyry, skarn, and high-sulfidation epithermal (see Figure 1) associated with high-level, oxidized porphyry stocks in magmatic arcs.

Thermo Scientific portable XRF analyzers can be used in any stage of exploration, mining, and ore processing of various metals from Au to silver (Ag), Cu, molybdenum (Mo), Pb, Zn, antimony (Sb),bismuth (Bi), etc. Detection limits for base metals in these instruments are low enough to allow even non-geologists to analyze any geological sample from outcrops to drill cores and soil specimens.In addition to precious and base metals, other elements, such as potassium (K), calcium (Ca), titanium (Ti), and light elements [magnesium(Mg), aluminum (Al), silicon (Si), phosphorus (P),and sulphur (S)] can be assayed as well. This helps geologists in mapping the hydrothermal alteration zones of the exploration/mining area or with 3D modeling of the alteration and mineralization.

JohnnyD
2 years ago
JohnnyD 2 years ago

All the above is all very well, but unless one has actually mapped the rocks geologically at the tenement or prospect level one does not have adequate ground-truth for accurate interpretation of either geochemistry or geophysics. In the case that stimulated the beginning of this thread, what is the known geological situation? All we know is that there is nuggety ground above mica schist.

John Koenig
2 years ago
John Koenig 2 years ago

I agree, we need first geological mapping, check if you have if you have sulphide so associated with gold bearing quartz veins. Then you can decide what techniques you could use.

The thread initiator says - Gold Exploration : Geophysical Methodology?
We have a situation - Mica schist has quartz veins and the quartz veins has gold?

JohnnyD
2 years ago
JohnnyD 2 years ago

A simple case history. I once worked on a prospect that had engaged the attention of a 3-4 month helicopter-supported camp in a very remote area, simply because a geologist had found a gold nugget in the nearby stream bed next to a chalcopyrite-rich cobble. The company had also run a soil survey across the prospect and had an excellent gold anomaly, forming what could be interpreted as a linear structure.

Whilst putting a costean across this interpreted structure as requested I walked 150m upslope of no exposure to a flat area and noted that the angular pebbles in the soil became rounded as I went uphill. I walked across the flat area and in one of the very shallow gullies crossing it I saw a cobble conglomerate containing cobbles with considerable chalcopyrite and identical to the one found earlier downslope. The flat area was quite clearly underlain by a perched river terrace containing imbricated chalcopyrite-rich cobbles and, doubtless, gold; it was a palaeoplacer deposit. And yet the company involved had spent a huge amount of money on and around the area when the answer was 300m away from the gold nugget. And that is not the first time I have encountered that sort of situation. Yes, there was a potential porphry-related deposit somewhere in the area, but probably some kilometres upstream where no geologist had gone.

Moral: active boots, with good eyes, on the ground to do good mapping and to ask awkward questions first, digging holes and costeans if one has to. Of course, broad-scale geochemistry, geophysics and assorted remote-sensing techniques can also be good pointers as to where to put boots on the ground, but for such a prior study of all legacy data is required first.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

I agree with this but if you really want a geophysical method resistivity might pick up the quart veins as lows depending on the size and continuity.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

You are right Johnny. I am now working in a prospect area in West Papua. The prospect area mainly consisted of boulders and clasts in the gravel show strong mineralization with massive pyrite found in graphitic slate and phyllite. Quartz veining, vuggy quartz and silicification are well developed in the same rocks. There is widespread iron staining and oxidation seen in boulders and disseminated pyrite, chalcopyrite, sphalerite and galena occur in the slate with quartz veins. Local miners are mining these materials for the gold nuggets which are related to Paleo Placer Deposit with a possibility of porphyry and skarn- replacement deposit in the explored area. 

Victor Bergman
2 years ago
Bill Fraser
2 years ago
Bill Fraser 2 years ago

Ground magnetic method, along with EM method, will be sufficient to delineate the quartz veins. Though, neither the quartz vein or the mica schist is magnetic, but they both have magnetic susceptibility contrast which may help delineate the boundary between the two. The magnetic method may serve as a reconnaissance survey, while the structural delineation of the quartz veins may be carried out with EM methods.

JohnnyD
2 years ago
JohnnyD 2 years ago

And if the mica schist carries metamorphic magnetite and pyrrhotite in specific horizons? Having seen drilling of barren anomalies based exactly on that.

David Kano
2 years ago
David Kano 2 years ago

What kind of gold deposit ? I think before carrying out your applied geophysical exploration method , firstly you do need an exploration geologist with his geological compilation work map where you can see outcrop geology map with regional and local structural control map and geochemical anomaly map, topographic map , a soil sampling gridding map, and to determine surface type of mineralization first, then it may be clear for you to carry out your ground geophysical survey work and trying to determine the sub-surface geology which must be connected to the surface geological data compilation.

JohnnyD
2 years ago
JohnnyD 2 years ago

With respect to gold. It is mobile in solution. The nuggets referred to may not be indigenous to where they have been found and could be very young; I am dealing with an identical situation in Queensland, Australia, where 1-9gram nuggets appear to have formed a few centimetres down in soil from solutions that have passed through spoil mounds raised by alluvial miners 100-150 years ago. That is the fundamental issue in this thread. The prospect described at the start of this thread consists of nuggety gold in 30cm of soil above mica schist. The presence of such gold nuggets does not necessarily indicate ANY gold in the underlying rocks. So turning to geophysics to test for ore bodies is, with the knowledge given to this thread, a pointless exercise. 3D IP, conductivity etc are all valid methods, but all are inapplicable for the given stage of knowledge of this occurrence. For the Queensland situation I am presently working on, it is assumed but not proved that the alluvial gold dug out 100-150 years years ago was indeed hosted originally in the geological structure, and it may be that the pattern of alluvial pits is a reflection of the geological structure such as we an determine form limited outcrop. However, until we drill, or dig costeans ,we are not going to know the truth of the matter.

Alan Carter
2 years ago
Alan Carter 2 years ago

The host rock from where the gold got disintegrated and subsequently deposited in the alluvial cover and or soil need to be identified and ascertained. The gold that is with the rock in all likelihood structurally .controlled. Endorsing Nassey's views the structural features to be properly assessed and subsequently demarcated. This is required to begin the search for the streams and other such source which carried the disintegrated gold particles/ nuggets.from the source.

Subsequent suitable geophysical( IP) method can more precisely delineate the features like structural features, burried channels etc

Helena Russell
2 years ago
Helena Russell 2 years ago

You may try ground spectrometry Gamma ray (radiometric eU, eTh and K) to delineate intrusion, that method could lead you to identify your quartz veins inside the bedrock (with high value of eTh and eU).
I have no direct knowledge or experience with Gamma Ray Ground Spectrometry{=radiometric eU. eTh and K}. If this method can discriminate intrusions and thence the quartz veins inside the country rock, with eTh and eU values anomalously high, so as to target some chances of gold-quartz reefs; the experimentation is worth trying. I have heard that the big-sized intrusives only can be only demarcated by this method, with some degree of confidence.
There is one method to search. Make pits not more than 2 mts pits. Each pit have distance /spacing 1/2 mtr. In line made 5 to 6 pits. We can easily get quality & quantity. This is also one kind of method. Made that kind of practice to open your mine.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Ground Gamma Ray Spectrometric Survey are excellent too for minerals that contain radioactive elements. It's a direct tool for searching radioactive minerals. But it is also effectively used in indirectly mapping igneous and sedimentary rocks based on their broad correlation with Potassium and SiO 2 (Galbriath and Sanders). Having said this, quartz veins contains gold and other sulphide so rarely contain Radioactive miners, hence it has negative correlation.

Further there are quartz veins that contains radioactive minerals and close geochemical assemblages like REE, Be, Zr, NB Ta, Cs etc. it also depends on the vein dimensions and density and extent. It also needs to be noted that gamma radiations can be picked up from first 30 cams soil, deeper source is difficult. I think depending on the associated sulphide minerals suitable geophysical methods and resistivity surveys can be used to trace Quartz veins bearing gold. Sometimes conventional trenching can help mapping the Quartz veins and their geology and mineralization. Shanti Kumar Chiluka Hyderabad & California

Helena Russell
2 years ago
Helena Russell 2 years ago

Like the proverbial belief of Voltaire, "I disapprove of what you say, but I will defend to the death your right to say it", quoted from Voltaire's biographical book in English by Evelyn Beatrice Hall (28 September 1868 – 13 April 1956), who wrote under the pseudonym S. G. Tallentyre, was an English writer best known for her biography of Voltaire entitled 'The Life of Voltaire', first published in 1903. welcome your opinion, dear Jon Moz Nassey.

We've discussed some direct and indirect geophysical approaches for gold in this column above.

Based on my working experiences in Oil Exploration and Mineral Exploration, in which it is clear that a geophysicist play the important role in Oil Exploration, while in the Mineral Exploration an exploration geologist play the important role. Regarding gold exploration, I think that every geologist knows that the best exploration approach will be Geochemical Exploration with a combination of detailed geological mapping. Sometimes we geologists don't need Geophysical Survey Data to decide where we have to put our Exploration Drill Location Holes, because the Exploration Geologist feelings based on their field work experiences are the best. The Big Freeport MacMaron Gold-Copper Mine in West Papua and the Big Ok Tedi Gold-Copper Mine in PNG are discovered by Exploration Geologists by Geochemical Exploration Approach.

JohnnyD
2 years ago
JohnnyD 2 years ago

For regional exploration, all techniques are valid including thorough research and reinterpretation of legacy data. However, over-reliance on geophysical and geochemical interpretations can skew thinking. It is essential that good geological mapping is carried out so as to constrain the imaginings that may arise from any remote sensing techniques. Geologically unsupported imaginings derived from geophysical and geochemical techniques can prove disastrous to a company's share value.

David Kano
2 years ago
David Kano 2 years ago

"Good geological control for Interpretation is a pre-requisite" Having said that I would say a magnetic survey (ground or airborne depending on scale) would be best to identify structures if there is a structural control to mineralisation (highly likely). If you correlate this with soil geochemical anomalies you might find some nice targets.

Geology first then Geophysics. That is why Geological Mapping with a combination of Geochemical Sampling first to establish a good Geological Compilation Data with Maps, then combine it with a Geophysical Survey Data. Exploration for Gold the geologist have to determine the type of deposit first : Primary Gold, Elluvial Gold, Colluvial Gold, Modern Alluvial Gold or Paleo Placer Gold or Old Terrace - Bearing Gold?

If there is outcropping geology the first/best/cheapest thing is detailed mapping and sampling. Here in West Australia many gold terranes are completely hidden under dozens to hundreds of metered lateritic soil so this isn't available as a first option.

JohnnyD
2 years ago
JohnnyD 2 years ago

West Australia. Regolith. Biogeochemistry?

Helena Russell
2 years ago
Helena Russell 2 years ago

The primary gold in your project area may be hosted by your mica-schist bedrock geology, particularly associated with zones of pyritized paragonite albite schist or quartz muscovite clinozoisite pyrite schist or quartz muscovite sulphide veining schist based on my geological survey work in West Papua. A pyritized paragonite albite schist sample have returned 330 gpt Au and 30 gpt Ag. All samples of quartz muscovite sulphide veining schist are gold-bearing, such as : > 2.50 gpt Au, 39 gpt Ag and 0.30% Cu. So, you need an experienced exploration geologist to determine your mineralized - gold bearing quartz muscovite sulphide veining ( f.g. pyrites ) outcrops, combined with geochemical sampling ( channel sampling and trenching sampling) and soil sampling within the mapped mineralized zones and to determine the local structural control on your mineralized zones. Then you may establish your ground- geophysical survey work ( IP?) after you have produced a geological compilation map over your mineralized area.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

This caption, "Good geological control for Interpretation is a pre-requisite", is nice however my answer to this is yes, with the rider that the term 'Good' is relative with varying meanings to varying interpreters.

Your previous comment has the use of a word 'terrane', which I suppose is meant for "terrain". In anticipation of approval, I shall put the differential aspects, as under:

Terrane is a related term of terrain and has some original connotations, as follows:
In context|geology|lang=en terms the difference between terrane and terrain is that terrane is (geology) a block of the earth's crust that differs from the surrounding material, and is separated from it by faults while terrain is (geology) a single, distinctive rock formation; an area having a preponderance of a particular rock or group of rocks.

As nouns the difference between terrane and terrain is that terrane is (geology) a block of the earth's crust that differs from the surrounding material, and is separated from it by faults while terrain is (geology) a single, distinctive rock formation; an area having a preponderance of a particular rock or group of rocks.

Presently A TERRANE in geology is a shorthand term for a "tectonostratigraphic terrane", which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of the surrounding areas – hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

Coarse gold is wonderful , so studying size, shape, etc. might be a good start. If you can do bulk testing that might be a good start. Outcrops are not always available to map. Is there a soil horizon where you are finding this material? Special Publication 25 Montana Bureau of Mines outlines some procedures and things to look at on initial studies.

Many years in prospecting for gold nuggets that lead us to locate the gold veins. One of the most effective methods was to use a French team excelentrs results, combined with Minelab GPX 5000 maintaining a balance of constant adjustment . What vombinas magnetometer to locate the vein . Going up the river or leaving the area combined quadrants . Magnetometry and French team are successful. Sometimes we use a blanket on the ground to locate nuggets.

If the locational details, geomorphology, rock types, structure and stratigraphy as well as the nature of gold veins, hangingwall footwall geology etc. are not told; the Minelab GPX 5000 balancing and constancy of adjustment etc. leading to magnetometric vein-catching, neither understood nor even appreciated. Hope, this enquiry does not go into undue inquisitiveness.

Yes, it seems you are dealing with orogenic gold deposit. if there are coincidence of gold and disseminated sulfide mineral like pyrite, arsenopyrite, chalcopyrite, conducting IP and complex resistivity are suitable geophysical investigation for your purpose.

JohnnyD
2 years ago
JohnnyD 2 years ago

Gentlemen. All we know of this prospect is that it consists of nuggets of gold, found by a metal detector, in 30cm of soil above mica schist. Trying digging some costeans below the nuggety zone to see if there are quartz veins in the mica schist, if there is minor non-economic gold in quartz sweats in the mica schist, or if indeed the gold is not overlying the source and the mica schist is barren. Once that is understood, then one can either do more geology backed up as needed by assorted geophysical techniques, or walk away not having wasted too much effort.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Do first detailed geologic mapping then grid soil sampling then trenching before you apply the more expensive geophysical survey.

John Koenig
2 years ago
John Koenig 2 years ago

Complementing geological mapping, Resistivity / IP is a must, particularly OreVision IP which delivers resolution & depth of investigation. The most popular technique now in the Abitibi Belt, both for precious and base metals.

Helena Russell
2 years ago
Helena Russell 2 years ago

If gold is in nuggets, may be it has suffered dragging and asociation with magnetic minerals it is possible and you can use magnetic methods.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

Gold nuggets just 30 cm below surface - productive horizon.- Very enigmatic situation. Is the gold within zone of weathering or in colluvium or in soil (residual) or alluvium? From where the gold possibly have come? JohnnyD's comment about mobile gold cannot be ignored. What happens to downslope slope wash is also auriferous? Really need some more info from you to understand the situation.

Quite possible that topographical displacements could have pulled down the gold nuggets. Iron Ore reeves often have valley plains full of loose or petrified clasts, gravels and even boulders of good iron ore, rolling down and forming 'Canga' bed.

Alan Carter
2 years ago
Alan Carter 2 years ago

The geophysical method to be applied for gold exploration will vastly depend on geological inputs defining nature of mineralization which will also include other minerals associated to decide the geophysiclal methods keeping in view interferences caused by such association.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Absolutely!

The geological exploration is to determine the surface geological data, and the geophysical exploration and core drilling are to determine the sub-surface data based on the surface geological data. Assume that the surface data have confirmed that the deposit is a skarn-replacement type deposit then I think that the geophysical methods of magnetic and IP may be good to determine the Ore Body at depth which is usually consisted of Magnetite - Pyrite - Chalcopyrite - Bornite - Gold + Silver and others (?).

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Suggested to check the physical properties using a portable SCIP Tester or equivalent to measure changeability and resistivity. The MPP-EM2S+ Probe or equivalent will allow to measure Magnetic Susceptibility/Conductivity. Suggests to do so before spending lots of money on a ground EM or IP Survey... Will allow you to define what works best and get some answers quickly before spending lots of money in the field. Allows also to explain the anomalies drilled with the DDH core. There are no common rules because the properties of mineral change, even within the same mine.

John Koenig
2 years ago
John Koenig 2 years ago

I agree the aforementioned comments and that IP surveying could be suitable for that. However, only good results are obtained when subsurface architecture is known. In my experience, a combination of geomorphological analysis (which also allows rational planning of field campaigns )and geophysical surveying by electrical resistivity imaging and IP usually provides good results in the identification of structures that might accommodate primary mineralization. Once such structures are detected, core drilling becomes necessary to characterize their economical interest.

David Kano
2 years ago
David Kano 2 years ago

SOME say that Successful Mineral exploration is a combination of basics of geology, geophysics, geochemistry and other exploration techniques, but more than these things, it is intuitive ecological thinking, passionate geologist, creative use of techniques, economics, time and of course luck.

I would disagree about the 'Luck' factor. Any exploration either it be gold or another commodity deploys the use of models based upon empirical evidence. The adequate testing of these models may be perceived as luck, but most likely relate to the understanding, coherence and strength of those models being tested. In addition, as science is evolving and new discoveries come to light (i.e. regarding ore genesis characterization and technologies that may detect these) then previous models can be further elaborated upon and/or challenged due to their understanding at that time. Probability and success rate in part also relate to data quality, frequency and pattern recognition. Fluid migration is always a wild card.

However, point taken that 'luck' may historically been a draw card for a many explorer. Still, the odds of finding that needle among the hay can be better achieved by understanding relationships of neighboring hay stacks.

Creativity is the ability to use the information available and to re-arrange this with a different perspective.

JohnnyD
2 years ago
JohnnyD 2 years ago

The use of models can blinker thinking. It is best to acquire good geological data and then build the interpretation. If it fits a model so be it.

David Kano
2 years ago
David Kano 2 years ago

For ease of writing or you could say laziness - I refer to geological models/ideas, not resc models (which I think you are referencing?)

JohnnyD
2 years ago
JohnnyD 2 years ago

I was referring to the habit of some to obtain some incomplete information about a prospect and then put the prospect into a box labelled with the name of a deposit type without obtaining the full range of available information first. Of course, past empirical experience is extremely useful in helping us to ask questions and in pointing to indicators, such as alteration patterns, which is perhaps what you were suggesting? Resource modelling is an entirely different kettle of fish.

Helena Russell
2 years ago
Helena Russell 2 years ago

The given information is not enough of course. but based on it, I think that we should pay more attention about structural issues first of all, it is quiet possible to be related with sedimintary environments that deformed during long period. So we should use geophysic methods which can determine structural elements in the depth. it means you have to be done at least surface structural study and interpretation enough first of it.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

A model, by definition, must admit - in the spirit of same " geological philosophy" - others models/variants, whence each model fecundity, and in the same time, its the ephemeral character.

Well, on this topic of gold exploration, who already discovered a big gold mine, because I would like to know how he discovered the big gold mine based on outcrop geology, geochemical anomalies and trace elements , geophysics methods , airphoto interpretation or remote sensing interpretation on structural control , petrographic and mineragraphic studies , hydrothermal alteration patterns and selection of drilling targets .

At the END we must have to think in many options:

  1. are the veinlets are covered by soil or bedrock?, you must do magnetometry or gravimetry to identified the veinlets, it does mean that you will identify the gold;
  2. are the veinlets outcropping?, you must try with remote sensing trying to identified the lineaments associated ;
  3. You must apply the Crosta Technique (remote sensing) to identify hydrotermal alteration bodies;
David Kano
2 years ago
David Kano 2 years ago

It's mostly assumed. I was just commenting on the eagerness of the mass dissing in a thread about an emerging trend. The blog has a good point about getting extra readings using digital methods, it even agrees with ground truthing for now. I don't think even you doubt that it will take over eventually. Using a Brunton will become (if it hasn't already) one of the old skill sets that, if taught at all, is more a curiosity than necessity. Nobody uses Rotring pens to produce maps anymore or manual planimeters for resource calculations. Young geos wouldn't even know what they are, but when digital was taking those over, there were the inevitable "ooh, ahhh, you can't trust them digital thingies" as well. It might be better for the youngsters if methods of overcoming some of the current digital shortcomings can be overcome tare pitched. Or...Look, matey, I know a dead technology when I see one, and I'm looking at one right now!

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

I think a lot of the comments in here are just venting really. That and a jolly fine round of the confirmation bias we are all subject to. Most of them know what will happen and will and do use what they need to as soon as they need to.

I find one of the interesting aspects to this is the different focus and development path to that of the super packages lent to us by the mining engineers, surveyors and mathematicians. Even today companies like Micromine, Datamane, Slurpac, and their various related entities can get $10s of thousands for specialist packages to have the collected data stored, queried and displayed decently.

With the uptake of smartphones, things are very different. Apps that cost a minimal amount (particularly in the scheme of an exploration program!) are popping up all over the place. Some of them make more difference to how we work as moving away from a standard Lotus 123 spreadsheet did years ago, but for a fraction of the cost (maps with gps...). Sure, there are checks and balances needed, but for my money (the tiny bit available), I would rather have a couple of good geologists out there taking hundreds of structural readings and photos from multiple sites that could be a degree or 2 and 10 metres out than a few contacts/planes/lineations/trends in 2 outcrops measured very accurately.

When you have to site the drillhole, you will be running in more detail (at least in your head), but even then, there are not a lot of rocks where orientations of anything are going to be identical across more than a few metres anyway. Get the core out, then do it in detail (maybe with an app? 😛 ).

Don't worry guys, those older skills will still be appreciated and dazzling the youngsters for decades. But it is not so much your skill with a Brunton as the knowledge and experience that goes with it that counts most. That's what they pay you for.

David Kano
2 years ago
David Kano 2 years ago

I'm the roughly the younger generation. Myself and the people I work with have looked into the Iphone right down to finding out where the hardware is sourced from. I see a lot of people championing the Iphone compass. Few of them have mentioned the vast differences in hardware through the Iphone models, which makes me think people don't know enough detail for sweeping statements.

The hardware is designed to deal with dynamic movement fluidly. Static measurements are not the primary role. That is why it is inferior hardware to a properly constructed fot for purpose digital device. It is an Iphone, not a field tool.

I have had my SUUNTO MC-2 for 14 years. Never had to calibrate it once. Never forgot to calibrate it and wasted half a days work either.

The jury is out as to whether geology, digital or otherwise will be playing any part at all in the future of the industry. The role is shrinking all the time, and geological input in resource estimation is now optional. As a discipline, it is going to get harder and harder to justify our existence. Of the changes that have occurred in the industry, how many can demonstrate a impressive results?

The fact that a compass does not have a processor is its major advantage. It is a simple elegant tool. You can spend all the money you like emulating it digitally in an Iphone and if you manage it, what you end up with is a compass. A digital one, with a data logger, but these have been around for many years.

I have a SOG multi tool. It is a superb piece of engineering. It has bad pliers, bad screw drivers, a bad knife, and a range of other tools which compared to a stand alone, designed for purpose item are just junk.

But the convenience of having a very poor but functional tool kit in a single pocket sized tool has advantages which out weight the short comings of each individual tool.

This is why the Iphone has no future as a professional tool. It has a bad gyroscope, a bad gps, a bad accelerometer, a bad magnetometer. Having all those things in a little hand held device makes a fantastic consumer product.

A geological compass is optimised for the task you buy it for. Any tool in an Iphone is an afterthought of an afterthought of an afterthought.

The old timers are copping it for being backwards. But I really think if you are pursuing the Iphone, you need to do more research. There are better tools of commercial quality out there. Better sensor configurations, better GPS capabilities.

Using a phone is not where we are headed. It makes zero sense to try and fit all your tools into one device. I have a workshop full of tools. Hundreds of them, each specialised so they can carry out a specific task efficiently. We will carry some kind of personal digital device, or several. But it makes vastly more sense to slave made for purpose tools wirelessly to the processor in your pocket.

I also don't really see the great enthusiasm for automated measurement recording. It records the easting and northing, and the dip and dip direction. That is great, but that is 2 out of at least a half dozen other entries minimum. Non-attributed measurements will be deleted (if I ever see them). So the time saving over a traditional compass is quite minimal. Not sufficient to justify the loss of accuracy and precision.

How will you know the fold you find with your iphone measurements and statistics is a fold? A consistent flaw in your digital device will give you the same thing. Your Iphone does not have hundreds of years of flawless performance to establish trust. Why should I believe you are all? Can you demonstrate any validation of your statistics, so you know for certain it is not just an artefact of damaged hardware?

Bill Fraser
2 years ago
Bill Fraser 2 years ago

From an Australian point of view the most tried and true method for structures is an airborne/heli-borne magnetic/radiometric survey likely with 50m line spacing for enhanced detail. Most gold here is structurally controlled so airborne magnetic is very good for that. In addition you get an accurate DEM and as structure usually defines topography this is also helpful.

I also agree with the wall-rock alteration comment and there are numerous devices that can measure alteration mineralogy in real time ie PIMA and so get vectors to gold in that way.

Either way you have found gold so that's good rather than wondering where it is.

Ace Levy
2 years ago
Ace Levy 2 years ago

Before one applies geophysics on the local scale as is the case here, try to understand the geology. Vein-hosted gold is not always accompanied by magnetite or pyrrhotite and in mica schist these minerals may occur as a secondary metamorphic products and create completely false targets. Structures do not necessarily show up in radiometric images. VTEM can pick up groundwater and give delightfully misleading interpretations. If one knows one has a gold-bearing quartz-vein system, then conductivity/resistivity can be very useful. In this particular case, first, dig a few holes to find if the nuggets are related to the bedrock or not. It's that simple.

Dizzy Flores
2 years ago
Dizzy Flores 2 years ago

This is correct- do some digging, find out what one is dealing with before using geophysics. Keep it simple and on budget. STOPA- Stop, Think, Observe , Plan--- Act !

Sugar Watkins
2 years ago
Sugar Watkins 2 years ago

Now the given information was recently updated, so in this vein type case it is very complicated to determine quarts veins and mica schist since they almost have same resistivity character. So I would suggest that dipol-dipole, total magnetic methods but we have to use it very carefully and there is need to be done some test line and interpretation for the results before. Then choose what is the best parameter and spacing. At the end of all, the geophysic can't play main role for this type of exploration work, we just can use its result for additional factor to compare, and structure will be more important.

Bill Rico
2 years ago
Bill Rico 2 years ago

I think magnetic gradient is good to detect quartz veins, easy and cheap.

Carmen Ibanz
2 years ago
Carmen Ibanz 2 years ago

Geophysical techniques depend on variations in the fields being being measured. Unless you have magnetic materials in the rock, you will get no response. Likewise electrical methods. Mica schist and quartz would have similar responses magnetically. Having consulted for a client who had wasted large sums of money on a considerable amount of cored diamond drilling, chasing barren magnetic and IP/resistivity/conductivity anomalies before doing adequate mapping (and that wasn't the first time that I had seen that kind of behaviour), I am all for doing good mapping and digging holes to see what is below the soil first. If the area is indeed covered in thick regolith then one has to use other techniques.

Interestingly enough, a good many gold mines have been found by prospectors who knew how to pan properly for gold and then dug holes in the right place.

Marshal Meru
2 years ago
Marshal Meru 2 years ago

There are many methods of Gold exploration. Mainly Geological, Geochemical and Geophysical. I have seen the discussion of the above and you may follow accordingly geophysical methods suggested by them. The mineralogical associations of gold should be established first. The gold deposits have been formed in different geological and geochemical environments. Hence different mineralogical associations prevail. Example: In India, gold exploration in Veligallu schist belt, Mineral pathfinders have been established during heavy mineral investigations along the primary and secondary and tertiary streams. When started inspecting the heavy mineral concentrate samples we have seen the presence of Scheelite, Monazite and gold together due to mechanical concentration as their densities are similar. As the Monazite radioactive we did gamma ray spectrometer survey and found the spots of sampling locations. Hence one show know the Mineral associations for further investigations.

rajesh
1 month ago

sir can u give some more information about velligallu schist belt exploration technics?

Jean Rasczak
2 years ago
Jean Rasczak 2 years ago

Please conduct proper geological survey and if you find some exposure of quartz vein and bed rock then no need to conduct geophysical method. You can have some trenches to explore the area. Geophysical method will not help much for quartz vein related gold deposit. But of course if you find some sulfide mineral then can conduct magnetic and IP survey to see structural behavior and demarcation of Ore body.

Arman
5 months ago
Arman 5 months ago

hello guys. In a resistivity pseudosection, gold shows low resistivity. But if the gold is volcanic hosted, how do we detect the gld because volcanics have high resistivity.

line4 resist
https://www.911metallurgist.com/wp-content/uploads/2017/02/Line4-resist.png

Please join and login to participate and leave a comment.

BUY Laboratory & Small Plant Process Equipment

We have all the laboratory and plant equipment you need to test or build/operate your plant.

ENTER our Mining Equipment' Store

We Sell EQUIPMENT for all types of Mineral Treatment PROCESSES and Laboratory Testing needs

Have a Mineral Processing QUESTION?

Come in, ask your question

911Metallurgist Community Forums

Talk to other metallurgists and be helped.

Need ENGINEERING Services or Plant TROUBLESHOOTING?

We can IMPROVE ALL PLANTS / Mineral Processing Engineering & LABORATORY Ore Testing

911Metallurgy Engineering

Contact us for process engineering, metallurgical investigations, plant optimization, plant troubleshooting, needs. WE “FIX” METALLURGY.