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

Abstract

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...

REE in fluid inclusions of quartz from gold deposits of north-eastern Russia

“…This implies that the LREEs may be involved in the formation of strong REE carbonate complexes. Authors [17,20,21] show that the magmatic fluid prevails in some hydrothermal systems, but according to Banks et al [30] magmatic fluids contain higher REE concentrations (200-1300 ppm) in comparison with our data. However, granite melt during its ascent to the surface at different depths can be a source of magmatic fluids with various REE patterns differing from that of corresponding melt phases [31].…”

“…Long functioning of large hydrothermal systems involves fluids from different sources. Earlier complex investigations of these deposits [17,20,21] have shown the wide variations of ore formation parameters and heterogenic nature of ore-forming fluid. At the early stages the H 2 O-CO 2 -CH 4 -H 2 S-NaCl fluid of various salinity arrived in an ore-forming system.…”

“…The Upper Triassic sand-shale rocks deformed into an asymmetric anticline about 2 km wide which hosts the deposit. The SW limb of the anticline is complicated by the Adycha-Taryn regional fault consisting of two or three nearly parallel branches, the Ore Fault being the major one [20]. The plane of this fault dips to the NE (40…”

“…Fluid inclusion observations were made for quartz of different types in each deposit. Fluid inclusions can be divided into three types: (I) mixed CO 2 [17,20,21] and are summarized in Table 3. The primary inclusions are predominant both in number and in volume over the secondary inclusions, so the leachate is proposed to be dominated by the primary fluid.…”

“…The contributions of LREE and HREE are slightly decreased and the contribution of Table 3. Summary of fluid inclusion data after [17,20,21].…”