Characterization of Carlin-Type Gold Ore by Photoacoustic, Raman, and EPR Spectroscopy

Abstract

Low-grade carbonaceous gold ore (0.01 to 1.8 oz/ton of gold) from the Carlin mine in Elko county, Nevada, has been characterized by a variety of analytical and spectroscopic techniques with emphasis on vibrational spectroscopy. A particular concern was determining the nature of the carbon-containing material in the ore. It was found that in addition to the anticipated carbonate, finely disseminated elemental carbon is present in amounts ranging from 0.062 to 0.43 wt. %. Contrary to previous reports, no detectable amounts of humic acid materials or organic hydrocarbons are present in any of the samples investigated.

Implications of hydrocarbons in carbonaceous metamorphic and hydrothermal ore-deposit rocks as related to the hydrolytic disproportionation of organic matter

“…Friedman et al (1982) made similar hypotheses related to Russian disseminated gold deposits. Nelson et al (1982) extracted 50g of Carlin carbonaceous ore for 96 hours and reported obtaining only sulfur with no detectable HCS, in contrast to the results of Radtke and Scheiner (1970) and of this study. Our Soxhlet-extraction technique involves using a polished copper strip in the solvent-boiling pot to remove elemental sulfur (a standard procedure).…”

“…Thus, the lack of, or light, color of extracts from Carlin-type rocks predisposes one to assuming no bitumen exists in the extracts. also reported that no bitumen was recovered from solvent extraction of rocks, similar to those studied by Nelson et al (1982), but from Jerritt Canyon, thus seemingly confirming Nelson et al (1982) and negating Radtke and Scheiner (1970). Moreover, other analyses carried out by were interpreted as demonstrating that the carbon in their rocks was "burned-out" (overmature) and incapable of either generating, or being associated with, HCS.…”

“…However, the conclusions of Nelson et al (1982) and Levanthal and Hofstra (1990) regarding the highly-metamorphosed "dead" nature of the organic carbon in the orebearing shales of Carlin-type gold deposits would appear to be supported by the data of both and . Those studies presented ROCK-EVAL data of ore-bearing shales from various north central Nevada Carlin-type gold deposits.…”

“…Different studies have revolved around the pronounced association of large deposits of sub-microscopic gold in carbonaceous shales of northern Nevada ("Carlintype" gold deposits) including Radtke and Scheiner (1970), Nelson et al (1982), Hausen and Park (1986), Ilchik et al (1986), Pasteris et al (1986), , , and Hofstra et al (1991). Most of the publications concerning OM in Carlin-type gold deposits attempt to demonstrate that the carbonaceous OM of these shales caused the deposition of microscopic gold ore.…”

“…In fact, one of our samples still yielded elemental sulfur in the extract, which had to be cleaned before extract weights could be obtained. Separating elemental sulfur from the bitumen during extraction makes the extracted bitumen much more obvious, in contrast to the approach of Nelson et al (1982). Moreover, as discussed, we extracted our samples for 504 hours versus 96 hours, and in some of our other rocks, after 96 hours, significant amounts of bitumen were not yet recovered.…”