“Invisible” Gold in Pyrite and Arsenopyrite from the Pavlik Deposit (Northeastern Russia)

Abstract

The first study on the distribution pattern and features of the “invisible” gold concentration in pyrite and arsenopyrite was carried out for a typical gold–quartz deposit of the Kolyma region. It was established that the main concentrator of “invisible” gold on the Pavlik deposit is the Late Arsenian pyrite-2. The method of Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometer (LA-ICP-MS) gives an Au content up to 478 g/t; the Electron Microprobe Analysis (EMPA) gives up to 570 g/t by. The As content, determined by LA-ICP-MS is up to 4.1 wt % and up to 3.4 wt % by EMPA. Pyrite-2 overgrows and replaces the early pyrite-1 with a reduced content of As and Au. Microinclusions of the Pb–Zn–Cu–Sb–Ag–Bi–containing phases are concentrated at the boundaries of the pyrite-1 and pyrite-2 blocks. Pyrite-2 is depleted by an order in Cu, Zn, Ag, Sb, Pb, and Bi in comparison with pyrite-1. The max Au/As molar ratio in pyrite-2 is 0.006, which suggests the presence of Au in the form of a solid solution. In another case, pyrite, depleted by trace elements, is cemented with As, Ag, Sb, Au, and Pb-rich marcasite with native gold. In arsenopyrite, there is a homogeneous distribution of gold at low concentrations (up to 3 g/t) in euhedral crystals and a heterogeneous distribution (up to 7 g/t) in deformed fissured grains.