Geology, mineralization, and fluid inclusion characteristics of the Kumbel oxidized W–Cu–Mo skarn and Au–W stockwork deposit in Kyrgyzstan, Tien Shan

Abstract

The Kumbel deposit is located within a metallogenic belt of W–Mo, Cu–Mo, Au–W, and Au deposits along the Late Paleozoic active continental margin of Tien Shan. The deposit is related to a Late Carboniferous multiphase pluton, with successive intrusive phases from early olivine monzogabbro through monzonite–quartz monzonite to granodiorite and granite, with the latest monzogabbro–porphyry dikes. The deposit represents an example of a complex W–Cu–Mo–Au magmatic–hydrothermal system related to magnetite-series high-K calc–alkaline to shoshonitic igneous suite. It contains large bodies of W–Cu–Mo oxidized prograde and retrograde skarns, with abundant andradite garnet, magnetite, and especially hematite, as well as K-feldspar, molybdoscheelite, chalcopyrite, and molybdenite, with transitions to zones of intense quartz–K-feldspar (with minor andradite and hematite) veining. The skarns are cut by quartz–carbonate ± adularia ± sericite veins (locally sheeted) and stockworks bearing scheelite and minor Cu, Zn, Pb sulfides, as well as Au, Bi, Te, and As mineralization. The association of these veins with the oxidized skarns and magnetite-series intrusion is consistent with the general oxidized, intrusion-related W–Mo–Cu–Au type of deposit, with an affinity to the alkalic (silica-saturated) Cu–Au ± Mo porphyry deposits. The fluid inclusion data show the predominance of magmatic–hydrothermal aqueous chloride fluid during the formation of skarns and quartz–carbonate–scheelite–sulfide veins. The high fluid pressures (∼1,750 bars), together with their high temperature (up to 600 °C) and high salinity (∼50–60 wt% NaCl-equiv.), suggest the formation of skarns and quartz–K-feldspar–andradite–hematite veins under conditions typical of magmatic–hydrothermal transition (depth of ≥4–5 km) of intrusion-related mineralized system, possibly by exsolution of the fluids from crystallizing magma. The auriferous quartz–carbonate–scheelite–sulfide veins formed from high to moderate salinity (from ∼40 to <20 wt% NaCl-equiv.) and high pressure (from ∼1,200 bars to 850–900 bars) aqueous chloride fluids under decreasing temperature (from ∼370 to 120 °C). The massive deposition of molybdoscheelite in retrograde skarn and scheelite in quartz–carbonate–scheelite–sulfide veins could correspond to enrichment of fluids in Ca (up to 18–25 wt% CaCl2), likely from crystallizing magma.