New Mexico Mineral Symposium — Abstracts

Galena mineral separates were collected from 21 mines in the Organ district and analyzed by directly coupled plasma-atomic emission spectrometry (DCP-AES) for the elements: antimony (Sb), bismuth (Bi), silver (Ag), tellurium (Te), and lead (Pb). The purpose of this study was to determine if trace-element substitutions of those elements (except Pb) into galena would be useful for characterizing mineralization when coupled with fluid inclusion, petrologic, and alteration studies. Galena was also analyzed by electron microprobe to determine if trace-element contents of the whole-mineral analyses of galena by DCP-AES were due to discrete mineral inclusions or solid-solution substitution. Both mineral inclusions and coupled semimetal (Sb/Bi)-silver solid solutions were found in the galenas analyzed.

Galena mineral separates that contained tellurium detectable by DCP-AES invariably contained inclusions of both altaite (PbTe) and native tellurium. Altaite replaced galena and native tellurium then replaced altaite. Hessite (Ag₂Te) was detected by electron microprobe in small grains isolated in galena from the Hilltop and Quickstrike mines in no particular paragenetic relationship with altaite or native tellurium. These samples also had high Ag concentrations as-determined by DCP-AES. No tetradymite (Bi2Te2S) was detected in any samples from the Organ district, although it had been reported by previous workers.

Detectable silver contents in galenas were accompanied by detectable semimetal (Sb or Bi) concentrations determined by DCP-AES analysis. Very few mineral inclusions were found in these samples, suggesting a coupled solid solution between galena and Ag-Sb(Bi)S₂. The Ag:Sb(Bi) ratios in these samples were near 1.0 except in samples containing Te (which also contained hessite). The only sulfosalt inclusion detected by electron microprobe was tetrahedrite, from the Hornspoon mine (which had a Ag:(Bi+Sb) ratio of 0.10). No Ag-Bi sulfosalts were detected although samples with the highest silver values were accompanied by high Bi concentrations.

High bismuth and silver concentrations appear to have a weak correlation to higher temperatures determined by fluid-inclusion-homogenization methods. Bismuth-rich galenas also appear to be deposit specific, most common in skarn deposits. However, the exact mechanisms for the distribution of Bi-Sb and Ag in the galenas analyzed are unresolved. The galenas containing tellurium mineral inclusions appear to be the result of a tellurium-rich fluid overprinting of a previously formed sulfide assemblage. The progression of more tellurium-rich mineralogies (galena-altaite-native tellurium) suggests such an overprint at temperatures near 3000 C (as determined by fluid-inclusion¬homogenization temperatures in coexisting quartz).