Gold Extraction

De-Silverizing Bullion

The de-silverizing of base bullion is carried out in accordance with the principles of the well-known Parkes process.

The base bullion produced by the blast furnace department carries (apart from silver values) impurities, the chief of which are copper, antimony, and arsenic.

In order to more clearly indicate the grade of the base bullion, the following analysis, representative of a half-year’s production of base bullion, is submitted:De Silverizing Bullion

Ag………………………………………………..68.6 oz.
Au………………………………………………0.096 oz.

Before proceeding with the actual operation of de-silverizing, it is necessary that the impurities, copper, antimony, and arsenic, should be eliminated. This is accomplished in the following steps :

Removal of Copper from Bullion

Copper is largely present in the base bullion as dissolved sulphide, and this is removed by liquation in a reverberatory type furnace, of which the following are the essential details:

Hearth area…………………………………220 sq. ft.
Grate area……………………………………..31 sq. ft.
Ratio hearth area to grate area……………….7:1.
Capacity…………………………………………57 tons.
Working temperature………………..750° to 850° C.
Coal consumption per 24 hours…………2 tons.

The hearth of the furnace is encased in a steel tank 22 ft. 4 in. long by 13 ft. 4 in. wide by 2 ft. 10 in. deep ; the bottom of the tank is covered by a depth of composition conforming ….Read more

How to Setup a Gold Sluice

So this is a typical sluice, they vary slightly in design but overall the same basic principles are at play. The point is gold is heavy, we’ve said that before but we can’t say it enough, gold is really, really, really heavy. So whenever it has a chance to, gold is going to drop faster than anything else in the creek. So when you have water running across here, you see this little ripple here, this is called a ripple. This is a upturn piece of metal that forces the water to go up, when it goes up there is a vacuum created right here. And when the water goes up it rolls around and gold tends to stuck underneath that ripple. These are expanded metal, so this is going to be a much smaller version of the exact same thing. Where gold is going to get caught behind each one of these little ripples. So water flows across here against this bump, the water goes up and gold drops out underneath. Then it comes back down and hits each one of these little ripples made of expanded metal and it drops in behind each one of these little corners. ….Read more

Sluicing for Gold – Set up & Operation

And my pan now, what I’m going to do is, I’m going you down to that stinking river I was telling you about, it’s got a little bit of gold in there, don’t ask me where it’s at, because I’m not going to tell you. I’m going to show you the proper way to set up this sluice box, do some clean up and get some gold, so come on, let’s go.

Ok, so, what do we got. Alright now, if you going to be using a sluice box, what’s the first thing you got to do? That’s right! Grab a sluice box. This is a key 852- I love these things. Ah yea they’re a little big and they don’t fold down but I been using these type for years. Now I know they make all different type of ones that fold in and they’re collapsible. But I really like this one, it does a good job – it’s got good flow on it. So, next what you going to need? You going to need 5 gallon bucket. Now I see guys doing it without a 5 gallon bucket, but trust me, this makes a whole lot easier. Now, inside ….Read more

Carlin Style Mineralisation Deposit Examples


goldstrike deposit Carlin Style Mineralisation Deposit Examples at Goldstrike

This section on Carlin Style Mineralisation Deposit Examples will give you a quick run through of a couple of actual Carlin deposits to give an idea of their characteristics; we will begin with Barrick’s goldstrike deposit, it’s in the north of the Carlin trend. Gold strike is the mother and father of Carlin deposits and is responsible for Barrick being the biggest gold producer in the world today. As you can see the geology exhibits a number of our targeting criteria. It’s hosted in dirty carbonate rocks in the lower plate located just under the Roberts Mountain thrust. It’s in an anticline in the hanging wall of the post fault and old fault that can be demonstrated to have been active during sedimentation 500 million years before the mineralization was introduced. There’s also next pre-existing intrusive that probably played a major role in structurally preparing the rocks for mineralizing fluids. Gold strike is just one of a cluster of deposits in this part of the Carlin trend. The deposited as I said is a monster and ….Read more

Fire Assay Procedure

Fire assaying has been practiced since ancient times and has proven to be very reliable in the determination of precious metal. References to fire assaying are found in the old testament of the Bible and artefacts in past civilizations’ ruins. Assaying began to appear in French and English literature in the 12th century and from there spread to the rest of Europe shortly after. The substances that can be fire assayed can be ores, metallic solutions and any material that are thought to be containing gold and silver. It uses scientific methodology and it is branch of analytical and inorganic chemistry.

Fire assay procedures uses a combination of intense heat (1900 °F) that is produced by a furnace, dry reagents called fluxes, and bone ash containers called crucibles and cupels. One uses this combination to fuse the fluxing agents and to isolate the precious metals. The ability to fire assay a substance relies on a number of facts. First of all, the samples that contain gold and silver should be solubility in molten metallic lead and that gold and silver are insolubility in slag. Fire assay also relies on the difference in specific gravity between the two liquids, the molten lead ….Read more

Mesothermal and Greenstone Gold Deposits AKA Orogenic Geology Formation

online-geology-courseMesothermal gold deposits form half way up through the rise of the melt from the deep crust to the surface usually at a depth of less than 10 km but greater than 1 km. temperatures at these depths are generally somewhere between 450 degrees and 250 degrees Celsius. The term mesothermal veins is really a sack term, referring simply to the depth formation.  It pays little attention to the origin of mineralizing fluids. This group of deposits forms throughout the earth’s long history all the way from the earliest Archean, say more than 3.4 billion years ago right up until today.

As I mention these deposits go by several names depending on who you’re talking to:

  • Greenstone gold
  • Archean lode gold
  • Shear zone hosted gold deposits
  • Orogenic gold deposits

They are all referred to pretty much the same sort of deposit. Well known example of the group of deposits include:

  • Kalgoorlie Super pit in western Australia
  • Globe and Phoenix, Zimbabwe
  • Campbell Red Lake in Canada
  • Giant Yellowknife deposits in Canada
  • Ashanti and Obuasi in Ghana
  • Hemlo deposits in Canada
  • Las Cristina’s in Venezuela

Although somewhat unusual in characteristics the Hemlo deposit in Canada can also be included ….Read more

Gold Bullion Assay Procedure

The procedure for assay of gold bullion, as described has for its sole object the estimation of the percentage of gold present in the alloy, all other constituents being disregarded. In the first instance, the simple case of the assay of gold alloys containing appreciable quantities of only copper and silver will be dealt with. Refined gold ingots and the alloys used for coinage, and for almost all jewellery, come under this head. The effect of large quantities of other impurities and the precautions thereby rendered necessary will be discussed later.

The method universally employed is that of cupellation and subsequent parting. The gold bullion is cupelled with silver and lead, by which the greater part of the base metals present is removed as oxides dissolved in litharge, and an alloy of gold and silver left on the cupel. This is “ parted ” by nitric acid, which dissolves the silver and leaves the gold unattacked.

In the following the practice at the Mint is described, but the same description would apply, with very slight alterations, to the methods used at other mints and assay offices.gold_bullion_assay

The degree of accuracy now attained in most assay offices ….Read more

How to Make Gold

The purest gold obtainable is required for use as standards or check pieces in the assay of gold bullion. The following method of preparing it is now in use at the Mint. Gold assay cornets from the purest gold which can be obtained are dissolved in nitrohydrochloric acid, and the excess of nitric acid expelled by evaporation with additional hydrochloric acid on a water bath. The blackish-red fused product, smelling of chlorine and consisting chiefly of AuCl3. HCl, or HAuCl4 (chlor-auric acid), is then poured in a thin stream into a large glass vessel full of distilled water, and a solution of about 1 oz. of gold in each pint of water (1 gramme of gold in 20 c.c. of water) is formed in this way. After vigorous stirring the solution is left to settle, and at the end of about a week, the whole of the precipitated chloride of silver will have subsided to the bottom. The progress of the subsidence is easily watched. The particles fall at the rate of about 3 or 4 inches per day. The clear bright supernatant liquor is now removed by a glass siphon, and diluted to about 1 oz. of gold per ….Read more

Fire Assaying Gold Alloys

It is often impracticable to apply the ordinary parting assay to the examination of low-standard alloys of gold with other metals. These are then tested by various other methods, of which a summary is given below, the alloys being grouped in four series for convenience:

A. Alloys requiring scorification.
B. Amalgams.
C. Alloys containing members of the platinum group.
D. Tellurium compounds.

Scorification of Alloys

fire-assay-gold-alloys Fire Assaying

Alloys of arsenic or antimony are reduced to a fine powder and scorified with thirty parts of lead and a half part of borax. If the slag becomes pasty towards the end of the operation more borax is added, a little at a time. If the lead button obtained is hard, a second scorification is necessary, with the addition of more lead. There is some loss of gold in the slag.

  • Iron or Manganese Alloys
    The operation is tedious and difficult with these alloys, as they are difficult to fuse, having higher melting points than pure gold, and the oxides of iron do not form easily fusible compounds with the litharge. An extremely high temperature is required; ten parts of lead, one of borax, and one of silica ….Read more

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