So how do we explore for Porphyry Copper Deposits which are completely covered by barren younger rocks? Well let’s back up a bit, we know that porphyries form under large subduction related volcanoes and that most of these are located under the ring of fire around the subducting pacific plate another fertile subduction zone occurs … Read more
Here are images of gold ores rich in sulfides including arsenopyrite. Some of the ore types in these photos: https://en.wikipedia.org/wiki/Breccia https://en.wikipedia.org/wiki/Hornfels http://www.merriam-webster.com/dictionary/intrusion https://en.wikipedia.org/wiki/Limestone https://en.wikipedia.org/wiki/Volcanogenic_massive_sulfide_ore_deposit http://tinyurl.com/qcazwv8
Another submarine syngeneic sulphide deposits- the SEDimentary exhalative or SEDEX deposit. These are very familiar in genesis to the VMS deposits except they are not primarily driven by intrusions below but are instead products of dewatering and metamorphism of thick piles of accumulated sediments in ocean basins hence the “SED” part of the name, the “exhalative” portion of the name … Read more
Many of the techniques are similar to those, have described for other deposit types. We need to start by focusing our efforts in areas where there is evidence of major felsic to intermediate volcanism, as it’s this volcanism that drives the epithermal systems. We also needed to find an area that has not been too … Read more
High Sulphidation Epithermal Gold Deposits form in geothermal systems where hot acidic hydrothermal fluid directly from the intrusion, remains undiluted by ground water. Low sulfidation deposits on the other hand from a geothermal system in which the magmatic fluid is cooled and diluted by groundwater and the pH is neutralized at depth. The formation of … Read more
Porphyry deposits and Beer having something in common. Porphyry ore deposit form in large intrusions that acted as magma chambers feeding active volcanoes. You will remember that as the magma chamber cools from the outside inwards, barium, feldspar and quartz crystalize out so that the remaining melts becomes enriched in metals and volatiles. The volatiles … Read more
A fascinating group and characteristic of Epithermal gold deposits is that you can virtually see them forming today, simply by visiting hot springs. Like those with Yellowstone in Wyoming or Rotorua in New Zealand. This photo is Pamukkale, low sulfidation hot springs in Turkey, with a beautiful white centre terraces. If you like hot springs, … Read more
Being able to recover gold using a gravity method or process does not mean that gold is free and fully/completely liberated. For example, using Automated Digital Imaging System (ADIS) for Gold Search (ADIS is an optical screening and imaging equipment package customized to locate gold occurrences in ground sample), a sub-sample of 8 samples representing 8 lithology for an … Read more
If we start with VMS Volcanogenic Massive Sulphide Ore Deposits and their Mineralization we see from this image shows some of the sulphide chimneys associated with the model black smoker VMS deposit. VMS will emit black plume of hot water venting from one of the chimneys. You’ll remember this cross section from reads on both porphyry deposits and epithermal, … Read more
What does a Greenstone/Mesothermal shear zone hosted Mineralization deposit look like? Well they usually comprise one or more steeply dipping quartz or carbonate rich veins, as you can see in the pictures these sometimes forms veins or even stock works of narrow vein. Mineralization is regularly distributed in the vein often forming steeply plunging high grade. … Read more