Richard W. Hutchinson

Syngenetic Au on the Carlin trend: Implications for Carlin-type deposits

A new type of gold occurrence recently discovered in the Carlin trend, north-central Nevada, is clearly distinct from classic Carlin-type gold ore. These occurrences are interpreted to be of sedimentary exhalative (sedex) origin because they are stratiform and predate compaction and lithification of their unaltered Devonian host rocks. They contain barite that exhibits δ34S and δ180 values identical to sulfate in Late Devonian seawater and sedex-type barite deposits. Abrupt facies changes in the host rocks strongly suggest synsedimentary faulting and foundering of the carbonate shelf during mineralization, as is characteristic of sedex deposits. Gold occurs both as native inclusions in synsedimentary base-metal sulfides and barite, and as chemical enrichments in sulfide minerals. The absence of alteration and lack of δ13C and δ180 isotopic shift of primary carbonates in these rocks is strong evidence that this gold was not introduced with classic Carlin-type mineralization. Collectively, these features show that the Devonian strata were significantly enriched in gold some 300 m.y. prior to generation of the mid-Tertiary Carlin-type deposits. These strata may have been an important, perhaps even vital, source of gold for the latter. Although gold is typically low in most Zn-Pb-rich sedex deposits, our evidence suggests that transport of gold in basinal fluids, and its subsequent deposition in the sedex environment, can be significant.

Acceptance of the R.A.F. Penrose Gold Medal for 2004

Thank you sincerely, Poul, for your citation, and I have many others to thank for their assistance in my work. Firstly, thanks to you and all my students, both graduate and undergraduate, at the University of Western Ontario and Colorado School of Mines for their tolerance of, and interest in a sometimes overly enthusiastic espousal of my controversial ideas. I have learned more from their ensuing studies than I could then have thought possible. I am immensely proud of that result; it is a teacher’s highest award. Secondly, I have been hugely fortunate in supportive and knowledgeable instructors, colleagues and associates: Gordon Suffel, Bob Hodder, and Bill Fyfe at UWO; Gene Cameron, a former Penrose Awardee who supervised my graduate studies at the University of Wisconsin; Sam Adams, Graham Closs, and Sam Romberger at CSM, amongst others; and many distinguished colleagues throughout the world who have assisted significantly and cooperated in my work, especially Des Pretorius and his co-workers Carl Anhaeusser, Lawrie Minter, and Richard and …