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New mineralogical, thermobarometric, isotopic, and geochemical data provide evidence for long and complex formation history of the Sarylakh and Sentachan Au-Sb deposits conditioned by regional geo dynamics and various types of ore mineralization, differing in age and source of ore matter combined in the same ore localizing structural units. The deposits are situated in the Taryn metallogenic zone of the East Yakutian metallogenic belt in the central Verkhoyansk-Kolyma Fold Region. They are controlled by the regional Adycha-Taryn Fault Zone that separates the Kular-Nera Terrane and the western part of the Verkhoyansk Fold-Thrust Belt. The fault extends along the strike of the northwest trending linear folds and is deep rooted and repeatedly reactivated. The orebodies are mineralized crush zones accompanied by sulfi dated (up to 100 m wide) quartz-sericite metasomatic rocks and replacing dickite-pyrophyllite alteration near stibnite veinlets. Two stages of low sulfide gold-quartz and stibnite mineralization are distinguished. The formation conditions of the early milk white quartz in orebodies with stibnite mineralization at the Sary lakh and Sentachan deposits are similar: temperature interval 340-280°C, salt concentration in fluids 6.8-1.6 wt % NaCl equiv, fluid pressure 3430-1050 bar, and sodic bicarbonate fluid composition. The ranges of fluid salinity overlapped at both deposits. In the late regenerated quartz that attends stibnite mineralization, fluid inclusions contain an aqueous solution with salinity of 3.2 wt % NaCl equiv and are homogenized into liquid at 304-189°C. Syngenetic gas inclusions contain nitrogen 0.19 g/cm 3 in density. The pressure of 300 bar is estimated at 189°C. The composition of the captured fluid is characterized as K-Ca bicarbonatesulfate. The sulfur isotopic composition has been analyzed in pyrite and arsenopyrite from ore and metaso matic zones, as well as in coarse , medium , and fine grained stibnite varieties subjected to dynamometa morphism. The following δ 34 S values, ‰ have been established at the Sarylakh deposit: -2.0 to -0.9 in arse nopyrite, -5.5 to -1.1 in pyrite, and -5.5 to -3.6 in stibnite. At the Sentachan deposit: -0.8 to +1.0 in arse nopyrite, +0.5 to +2.6 in pyrite, and -3.9 to +0.6 in stibnite. Sulfides from the Sentachan deposit is somewhat enriched in 34 S. The 18 O of milk white quartz at the Sarylakh deposit varies from +14.8 to 17.0‰ and from +16.4 to + 19.3‰ at the Sentachan. The δ 18 O of regenerated quartz is +16.5‰ at the Sarylakh and +17.6 to +19.8‰ at the Sentachan. The δ 18 O of carbonates varies from +15.0 to 16.3% at the Sarylakh and from +16.7 to +18.2‰ at the Sentachan. The δ 13 C of carbonates ranges from -9.5 to -12.1‰ and -7.8 to -8.5‰, respectively. The calculated δ 18 O H 2 O of the early fluid in equilibrium with quartz and dolomite at 300°C are +7.9 to +10.1‰ for the Sarylakh deposit and +9.5 to +12.4‰ for the Sentachan deposit (+4.9 and 6.0‰ at 200°C for the late fluid, respectively). Most estimates fall into the interval characteristic o...

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 ...

Petrochemical characteristics of igneous, sedimentary, and metasomatic rocks; chemical and isotopic compositions of minerals and fluids; and PT parameters of mineral formation at the Nezhdaninsky deposit are reported. A model of hydrothermal system formation is developed on this basis. In addition to decreasing Ba/Rb and Li/Mg ratios in the course of the hydrothermal process, resulting in the formation of ore-bearing metasomatic rocks, increasing K/Ba and diminishing K/Cs ratios indicate the probable participation of magmatic fluid in the ore deposition. The agreement of the K/Rb and K/Ba ratios with the values typical of the main trend of igneous rocks (MT) implies that the K, Rb, and Ba contents were distributed in the ore-forming hydrothermal fluid according to the ratios in the source magmatic chamber. The K/Rb ratios in metasomatic rocks correspond to the MT and approach the pegmatitic-hydrothermal trend and the composition of orthomagmatic fluid of Mo-W greisen. Similar REE patterns of igneous and terrigenous rocks do not allow the REE source to be constrained unequivocally. The lithological control of lithophile element distribution testifies to the supply of host rock components to the hydrothermal system. All studied rocks and minerals are enriched in LREE. The REE total and the contribution of HREE decrease from preore to synore metasomatic rocks, from preore to regenerated carbonates, and from older to younger scheelite. A similar tendency is noted in granitoids of the Kurum pluton. The δ 18 O values of quartz range from +10.3 to +12.6 ‰ in Au-Mo-W zones, from +15.9 to +16.4 ‰ in metasomatic rocks, from +14.8 to +16.6 ‰ in gold-ore veins, and from +13.5 to +16.9 ‰ in silverbase-metal ore mineralization. The estimates of δ suggest that water was supplied from a magmatic source ( δ 18 O = +(5.5-9.0‰)) and as a product of sedimentary rock dehydration. High-temperature (up to 390°C ) and highly concentrated (up to 31 wt % NaCl equiv) fluids participated in the mineral formation. The phase separation of the fluid into H 2 O-CO 2 liquid and predominantly carbon dioxide gas was combined with mixing of a high-temperature and relatively highly concentrated chloride solution with a low-temperature and poorly mineralized fluid. The redox conditions varied from equilibrium with CH 4 -bearing fluid at the goldmolybdenum-tungsten stage to equilibrium with CO 2 -bearing fluid during the gold-ore stage.