Silver-Rich Chalcopyrite from the Active Cerro Pabellón Geothermal System, Northern Chile

Abstract

Active subaerial geothermal systems are regarded as modern analogues of low- to intermediate-sulfidation epithermal Au–Ag deposits, where minor amounts of Cu are mostly present as chalcopyrite. Although trace element data concerning sulfides are scarce in active geothermal systems at convergent settings, studies in several other environments have demonstrated that chalcopyrite is a relevant host of Ag and other trace elements. Here, we focus on the active Cerro Pabellón geothermal system in the Altiplano of northern Chile, where chalcopyrite-bearing samples were retrieved from a 561 m drill core that crosscuts the high-enthalpy geothermal reservoir at depth. A combination of EMPA and LA-ICP-MS data shows that chalcopyrite from Cerro Pabellón is silver-rich (Ag > 1000 ppm) and hosts a wide range of trace elements, most notably Se, Te, Zn, Sb, As, and Ni, which can reach 100 s of ppm. Other elements detected include Co, Pb, Cr, Ga, Ge, Sn, Cd, and Hg but are often present in low concentrations (<100 ppm), whereas Au, Bi, Tl, and In are generally below 1 ppm. Chalcopyrite shows a distinct geochemical signature with depth, with significantly higher Ag concentrations in the shallow sample (494 m) and increasing Cd and In contents towards the bottom of the studied drill core (549 m). These differences in the trace element contents of chalcopyrite are interpreted as related to temperature gradients during the waning stages of boiling at Cerro Pabellón, although further studies are still needed to assess the precise partitioning controls. Our data provide evidence that chalcopyrite may play a relevant role as a scavenger of certain metals and a monitor of fluid changes in hydrothermal systems.

Precious and Critical Metal-Bearing Assemblages in the Ann Mason Copper Porphyry Deposit, Yerington, Nevada

“…The reduced capacity of chalcopyrite in the presence of bornite to partition trace elements is reflected in our data, with only 5-6% of hessite and electrum microparticles in the Ccp-Bn zone hosted by chalcopyrite. The majority of microparticles in the Ccp-Py zone are naumannite (Ag2Se) hosted by chalcopyrite, which is consistent with chalcopyrite containing an order of magnitude more Se than Te in solid solution (George et al, 2018;Reich et al, 2020). Se is also susceptible to fluid-rock interaction (Cook et al, 2011), so naumannite in the Ccp-Py zone may contain Se that has been remobilized and redeposited by fluids.…”

Rare and Critical Metals in Pyrite, Chalcopyrite, Magnetite, and Titanite from the Vathi Porphyry Cu-Au±Mo Deposit, Northern Greece

“…Pyrite and chalcopyrite can be associated with significant amounts or rare metals incorporated as nano-scale mineral inclusions or as nanoparticles [13,14,[18][19][20][21][22]24]. These inclusions can be formed due to exsolution from the pyrite or chalcopyrite matrix, as well as through precipitation from the hydrothermal fluid into the growing mineral [14,24].…”

Integration of geophysics and remote sensing techniques in mapping zones mineralised with disseminated gold and sulphide minerals in Lolgorien, Narok County, Kenya

“…An example of these clay minerals is argillicpropylitic clay minerals which are often associated with low electrical resistivity anomalies and they are formed as a result of the reaction between host rock and hydrothermal fluids (Fon et al 2012, Abbaszadeh and Hezarkhani 2013, Amer et al 2016, Moreira et al 2016. It is however, important to note that precipitation of adularia and quartz which usually accompany mineralisation of gold and silver commonly results into an increase of resistivity values exceeding 1000 Ωm (Fon et al 2012, Hedenquist and Arribas 2017, Cortês et al 2019, Reich et al 2020, Xu et al 2020). As such, gold mineralisation can be associated with both low and high resistivity depending on how and where the mineralisation process has occurred as is the case of Lolgorien (the study area) (Fon et al 2012, Moreira et al 2016.…”