The geological structural studies substantiate four stages of formation and activation of the fault network of the Southern Ashali gold deposit. Homogenization of fluid inclusions in quartz of the goldlow-sulfide-quartz ores took place at 338…147 °C. The salinity of the fluids varied from 10,5 to 0,3 wt.% with the dominant presence of NaCl and KCl. The sulfur isotope composition of pyrite-I (δ34S = -7 ‰) corresponds to a sedimentary source, and that of pyrite-II and arsenopyrite-I corresponds to a deep-seated source. The U-Pb isotope age determinations (LA-ICP-MS) on zircons from the granitoids 309.1 ± 2.1 and 305.8 ± 2.2 Ma, respectively, and the age of gold-low-sulfide-quartz ores is 280 Ma (Ar/Ar technique). A structural-compositional model of the ore deposit formation is proposed, that comprises six stages: I – sedimentation and early diagenesis; II – late diagenesis and/or metamorphism, associated with the gold-sulfide ores; III – effusive magmatism; IV – intrusive magmatism; V – hydrothermal-I, associated with gold-low-sulfide-quartz type ores; and VI – post-ore hydrothermal-II stage.
Microinclusions and impurity elements were studied in woody tin from the Kheta deposit in the Magadan Region. The ore deposit is situated within the Kheta volcanic-tectonic depression at an intersection of large zones of regional deep-seated faults and belongs to the tin-sulfide industrial type of the ferruginous-polymetalic-tin ore formation. Electron microscopic studies (SEM) of the woody tin revealed microinclusions of rutile, ilmenite, quartz, aluminosilicates, and wolframite. By the LA-ICP-MS technique, 25 impurity elements with the contents above 1 mg/kg were found in the woody tin. Most of the elements were recorded in rare measurements with the contents less than 10 mg/kg. In the range of 10–100 mg/kg, the average concentrations of K, Sc, Mn, Cu, Zn, Ga, Zr, Pb, and Bi were established; in the range of 100–1000 mg/kg, the Ti, Y, and Sb concentrations; and above 1000 mg/kg, the Al, Fe, and W ones. The concentration distribution features and correlations of the impurity elements were determined mathematically. Assumptions are made on the entry of these impurities into the cassiterite structure and on possible mineral microinclusions.
A potential effectiveness of IR microscopy in application to forecasting and prospecting for base and precious metals deposits is demonstrated on examples of studying zircon crystals collected at the Mechiveem area (Okhotsk-Chukotka volcanoplutonic belt), Sukhoi Log ore field, and Natalka gold deposit. An important typomorphic characteristics of zircon, that is determined by IR microscopy, is the degree of structural perfection of the crystals. This diagnostic feature depends on the composition, age, and crystallization conditions of the mineral and serves as one of criteria for distinguishing its generations in exploration areas with multiple zircon sources. For example, in areas of distribution of potentially goldbearing carbonaceous-terrigenous complexes, newly formed metasomatic zircon whose age coincides with the main ore formation stages is of forecasting and prospecting significance. One indicator of the zircon hydrothermal transformations intensity, determined by its IR spectra, is the relative content of adsorbed water in the crystal. This feature is most effective for prospecting in areas of relatively young volcanic and intrusive formations.
The article provides a brief geological description of the Southern Ashaly mineral deposit within which ores of the gold-sulfide and gold-low-sulfide-quartz types were recognized. Two ore mineralization phases were established, that incorporate four stages, the pyrite, pyrite-arsenopyrite, sulfide, and polymetallic ones. The morphological and mineralogical-geochemical features of the major, minor, and rare ore minerals were studied in detail. The following successive generations of pyrite were established at the deposit: diagenetic, metamorphic, and hydrothermal, that embrace six varieties with its own geochemical features. Elevated concentrations of gold in diagenetic pyrite have been recorded and visually confirmed. Native gold of two generations is formed at the pyrite, pyrite-arsenopyrite (early), and sulfide (late) stages and have an average gold fineness of 884 and 998 ‰, respectively. The temperature of transformation of the carbonaceous matter of rocks of the Bukon Formation and of generation of the ores of the gold-sulfide type varies from 384 to 241 °C, which corresponds to the greenschist-zeolite facies of metamorphism.
The paper presents the first U–Pb data (LA-ICP-MS method) on zircon from rocks of the intrusive massifs of the Middle and Southern Tien Shan associated with tungsten deposits of various metallogenic types. Age frontiers of the intrusion emplacement in different tectonic segments of the Tien Shan orogenic belt are established. These age frontiers correspond to certain variations of the tectonic settings, which occurred during the Late Carboniferous-Permian post-collisional stage of the development of this orogenic belt. In particular, the emplacement of the high-potassic intrusions associated with tungsten-molybdenum-copper-gold deposits in the Naryn and Terskey segments of the Middle Tien Shan occurred in the post-collisional setting soon after the termination of active subduction, in the intervals of 325–302 Ma to 303–283 Ma, with the notably younger dates in the western direction. The high-potassic intrusions associated with similar tungsten mineralization in the Kurama segment of the Middle Tien Shan were formed in the similar age interval (298–290 Ma) and significantly later than the high-potassic igneous suites accompanied by copper-molybdenum-gold porphyry mineralization. In the southern (Gissar and Zeravshan) segments of the Southern Tien Shan, two age intervals are distinguished for the intrusions associated with tungsten-polymetallic(-gold) deposits: (i) Late Carboniferous-Early Permian (from 307–298 Ma to 292–284 Ma) and (ii) Early Permian (in the order of 293–281 Ma). Tungsten-tin deposits are present in the same mineralized districts, with their intrusions also varying from the Late Carboniferous (305–300 Ma) to mostly Early Permian (296–290 Ma). The latter highlights a different metallogenic specialization of nearly coeval igneous suites at the post-collisional stage, with the participation of magmatic chambers formed in a different protolith in relation to magmatic sources at different crustal and upper mantle levels. The intrusive massifs associated with tungsten-molybdenum deposits in the northern (Nurata) segment of the Southern Tien Shan were formed during the total interval of 282–266 Ma that corresponds to a more mature post-collisional stage.
