Invisible Metals in Sulfides​

In a significant proportion of economically highly payable gold deposits, gold is not visible, be it with the naked eye or with high powered microscopes. Such gold is colloquially referred to as invisible gold (inv-Au).

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This inv-Au can be present in a number of deposit types, with the most famous being the so-called Carlin-type in which effectively all gold present occurs as inv-Au. 

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We have been investigating how gold (a geochemically simple element) incorporates into pyrite in Carlin type deposits (a very well understood system), in order to apply this knowledge forward to more complicated elements (Te, Se, Ag, In, Ge, Ga, etc.) in less understood deposits. 

 

We have been applying our fundamental research to more applied projects, including cleaning up sulfide minerals from historic mine waste as well as working with companies to de-sulfidise their tailings, to maximize their profits but also to keep these sites from being an environmental problem years from now. 

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X-ray maps of gold containing arsenian-pyrite rims from Nevada. 

(from Gopon et. al, 2019)

​​Using atom probe tomography (APT) allows us to see the metals at the near atomic scale, determine the elements it is co-located with, and determine the isotopic signature of the surrounding sulfide mineral.  

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APT Datasets showing the distibution of iron, sulfur,

arsenic, and gold at the near-atomic scale.

(note gold atoms are drawn 2x scale for clarity)

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Our group has developed a number of techniques to extract powerful new information out of APT datasets, including a way to extract the S isotopic signature from pyrite. 

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We are actively working a variety of sulfide hosted deposits including:

-Carlin-type Au deposits in Nevada (USA), Yukon (Canada), and Guizhou (China);

-Invisible Co deposits in Namibia;

-Historical gold-copper and lead-zinc mines (Austria and USA) and the associated critical metals

-Mid-Continental Rift Assocaited Massive Sulfide Deposits, Great Lakes Region USA

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My group is also working on native copper deposits in Northern Michigan, which are the largest and most accessible source of copper in the USA, and which we suspect might be related to the sulfide deposits which occur in the area.

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