Hunting Homestake gold?s roots

Editor?s note: Communications Department intern Kailas Ledbetter of the University of Nebraska filed this story for Deep Thoughts.

Graduate geology student Jeff Steadman is hoping to shed light on gold?s complex journey into the Homestake formation?a subject still debated by geologists 136 years after the ore body?s discovery.

Steadman?s own journey to Homestake is rather complicated. He is originally from Maryland, but he is working on getting his doctorate at the University of Tasmania in Australia. His thesis requires research in the Black Hills of South Dakota. Steadman also is a member of a research group called Petrology, Ore Deposits and Structures, or PODS, which was started by Colin Paterson, a geology professor at South Dakota School of Mines and Technology (SDSM&T) in Rapid City. PODS does geologic studies at the Sanford Lab.

Geologist Bill Roggenthen of SDSM&T described one way gold deposits such as Homestake might form. Gold deep within the earth bonds with an ion such as chlorine in water. The solution rises toward the surface, where changes in pressure, temperature, or chemical environment cause the gold to deposit.

Steadman is exploring a different model, in which gold is picked up by organic matter and then incorporated into pyrite during sedimentation, forming pyrite-bearing black shale.  Then comes ?folding,? such as folding during the formation of a mountain range, combined with metamorphism, during which the characteristics of the rock change, over a long period of time, due to increased temperature and pressure. These processes transport gold toward the surface, where it is deposited in rock formations.

Roggenthen says it is reasonable that the gold might have been deposited in the Homestake formation as a result of a combination of these or other models.

Steadman has analyzed black shale in Homestake core samples, and he has found pyrite containing gold in the Poorman formation, another formation in the former Homestake gold mine. But he said he did not find enough gold to suggest that the model he is studying is a significant contributor of gold to the Homestake deposit. More research will be required, he said. And he believes further study is important. ?The more we know about any kind of ore deposit, the better chance we have of finding another like it,? he said.