The world-class Natalka gold deposit, northeast Russia: REE patterns, fluid inclusions, stable oxygen isotopes, and formation conditions of ore

Abstract

mined out from primary ore and 105 t from the Omchak placer, related to the Natalka deposit. The follow-up exploration of the deposit in 2004-2007 resulted in the estimation of resources at 1760 t with a Au grade of 1.7 g/t (Grigorov, 2006). This deposit is a typical example of orogenic deposits localized in collision belts composed of volcanosedimentary and terrigenous rocks metamorphosed under conditions of greenschist facies (Goldfarb et al., 2005).Abstract -REE patterns of hydrothermally altered rocks, fluid inclusions, and stable oxygen isotopes of quartz were studied at the Natalka gold deposit. Metasomatic rocks formed under decompression reveal gradual depletion in LREE and HREE relative to siltstone of the protolith. The HREE patterns of metasomatic rocks formed under decompression are uniform; an insignificant removal of LREE can be noted. The progressive extraction of REE with increasing alteration of rocks could have been due to the effect of magmatogenic or meteoric fluid. Because a Ce anomaly is absent, the participation of oxidized meteoric water was limited. The inverse correlation between the total REE content and the Eu anomaly value in altered rocks indicates a substantial role of magmatogenic fluid. The REE patterns of altered rocks formed under compression show that the role of metamorphic fluid was not great. All metasomatic rocks are enriched in LREE, so that the enrichment of fluid in LREE as well may be suggested. Three fluid compositions were captured as fluid inclusions: (1) H 2 O-CO 2 -NaCl-MgCl 2 with a salinity of 1.0-4.9 wt % NaCl equiv, (2) CO 2 -CH 4 , and (3) H 2 O-NaCl-MgCl 2 with a salinity of 7.0-5.6 wt % NaCl equiv. Compositions (1) and (2) coexisted in the mineral-forming system at 250-350 ° C and 1.1-2.4 kbar as products of phase separation under conditions of decreasing P and T . The interaction of this fluid with host rocks resulted in the formation of extensive halos of beresitized rocks with sulfide disseminations. The precipitation of arsenopyrite and pyrite led to the substantial depletion of mineral-forming fluid in H 2 S and destabilization of the Au(HS) 2-complex. The fluid with the third composition arose due to the boiling of the H 2 O-CO 2 -CH 4 -NaCl-MgCl 2 liquid and was responsible for metasomatic alteration of host rocks. The late mineral assemblages were deposited from this fluid at the initial stage of ore formation. The high methane concentrations in the ore-forming fluid were likely caused by interaction of hydrothermal ore-bearing solutions with carbonaceous host rocks. The δ 18 O values of quartz from quartz-scheelite-pyrite-arsenopyrite and sulfide-sulfosalt mineral assemblages vary from +11.6 to +14.1‰ and +11.2 to +13.5‰, respectively. The parental fluids of the early and late mineral assemblages probably were derived from a magmatic source and were characterized by δ 18 = +6.3 to +8.8‰ at 350 ° C and +3.6 to +5.9‰ at 280 ° C, respectively. The narrow interval of oxygen isotopic compositions shows that this source was homogeneous. The data obtained ...

The Sarylakh and Sentachan gold-antimony deposits, Sakha-Yakutia: A case of combined mesothermal gold-quartz and epithermal stibnite ores

“…The altered rocks correspond to beresite in composition and differ from classic beresites (Zharikov, 1987) by the abundance of arsenopyrite in combination with pyrite. The occurrence of arsenopy rite makes beresite close to the wall rock alteration and mineralized crush zones described at the Nezh daninskoe, Maiskoe, and Natalka deposits (Bortnikov et al, , 2004(Bortnikov et al, , 2007Gamyanin, 2001;Goryachev et al, 2008). In the inner zone of the metasomatic alteration that adjoins the ore controlling fracture, quartz and sericite are predominant up to the forma tion of thin zones of metasomatic quartz.…”

The Blagodatnoe gold-sulfide deposit (Yenisei Ridge, Russia): the nature of geophysical anomalies and the succession and causes of formation of petrophysical zoning

“…In (Goryachev et al, 2008) Sulfide sulfur is bound during the crystallization of pyrite and arsenopyrite, which causes a destabilization of the Au(HS) 2 -complexes and the formation of native Au (Goryachev et al, 2008;Pavlov and Pavlova, 1971). Formation of the petrophysical zoning in the ore generation.…”

“…A gold-arsenopyrite assemblage is widespread in the ores of gold-sulfide deposits (Genkin et al, 2002;Gavrilov et al, 2009;Goryachev et al, 2008). Productive (and arsenopyrite) mineralization at these deposits is isolated from the areas of the most magnetic (pyrrhotinized) rocks.…”

The role of dynamometamorphism in the formation of the Mukodek gold field (North Pribaikalie)

“…Процессы формирования золоторудных мес-торождений на северо-востоке России детально рассмотрены в целом ряде работ [Volkov, 2005;Goryachev et al, 2008;Ostapenko et al, 2013;Parfenov, Kuzmin, 2001;и др.]. На фоне достаточно детально изученных золоторудных объектов Чукотского АО, Магаданской области и восточной части Рес-публики Саха (Якутия) Северное Прибайкалье изу-чено значительно хуже, за исключением Бодайбин-ского района [Buryak, Bakulin, 1998;Ivanov, 2014;Lobanov, 1970;Chugaev et al, 2014;Kucherenko et al, 2008;и др.…”