PETROLOGY OF MINERALIZED AND NON-MINERALIZED SAMPLES FROMTHE RAILROAD DISTRICT WITHIN THE CARLIN TREND, ELKO, NV
District were analyzed using standard petrography, Environmental Scanning Electron
Microscope (ESEM), and cathodoluminescence to identify the relationship between
host rock and gold mineralization fl uids. The Railroad District, southwest of Elko,
Nevada, is part of the Carlin Trend, an area known from submicroscopic gold deposition.
Samples consisted of mineralized and non-mineralized limestone (Devonian Devils
Gate Formation), mudstone (Mississippian Webb Formation), sandstone (Mississippian
Chainman Formation), and fault breccias.
Areas of highest mineralization are the Chainman Formation and fault breccias
containing high amounts of Webb Formation, where two or more mieralization idicative
phases were observed. Mineralized Chainman samples have stilpnomelane, Fe-rich
pyrite, barite, and andalusite porphyroblasts. Gold concentrations within mineralized
samples range from 2-5 wt. % in the Chainman Formationand 2-8 wt. % in the fault
breccias. An apparent bimodal distribution of Au was found which refl ects the media
density that contains it (Fe-rich pyrite vs. quartz).
Elemental (Si, S, Te, Ca, Fe, As, Au, Ag, Ba, Al, K, Na, and Ti) data gathered
was used for mean weight percents and correlation coeffi cients calculations for both
mineralized and non-mineralized samples. Mineralized samples had high correlations
between (Fe-S), (Au-Ag), and (Ti-Ba), whereas non-mineralized had low correlations.
Both mineralized and non-mineralized samples had low mean arsenic. Little correlation
was found between As and S in the mineralized and the non-mineralized samples.
Cathodoluminescence microphotographs defi ned differences between mineralized
and non-mineralized samples. The presence of [RGB 79 132 169] Marina -colored barite
and [RGB 210 115 143] Chateau Rose-colored quartz. Mineralized samples were more
vibrant than non-mineralized samples, making them easier to identify.