Geology and geochemistry of the Kadamzhai and Chauvai gold-antimony-mercury deposits: Implications for new province of Carlin-type gold deposits at the Southern Tien Shan (Kyrgyzstan)

摘要

The Tien Shan Belt extends for over 2500 km, from western Uzbekistan, through Tajikistan, Kyrgyzstan and southern Kazakhstan to western China, and represents a part of the Altaid Orogenic Collage. The Tien Shan is one of the largest gold provinces on Earth and hosts several world-class gold deposits. The Turkestan-Alay and Southern Fergana regions, located within the South Tien Shan, host an important Hg-Sb mineral province with proven reserve of over 5 Mt Sb and 0.8 Mt Hg. In Soviet times, during the intensive study and exploitation of the mercury-antimony deposits, increased gold content of these ores has been noted. But the focus on only the main ore components (Hg-Sb), as well as the absence of "working" exploration geological and genetic models of Carlin type deposits, did not allow to fully assess the gold potential of the ore belt. Meanwhile, gold exploration in the region during the past two decades has identified a few deposits, now recognized as Carlin type. The studied Chauvai and Kadamzhai Hg-Sb deposits belong to the central part of the South Fergana antimony-mercury belt and, together with other Hg-Sb deposits (Abshyr, Khaidarkan), form a large ore province. They are located in the northern arms of the Alay ridge extending along the southern flank of the Kauzan antiform. The South Fergana antimony-mercury belt is commonly associated with the North-Katran regional deep fault (located between the southern edge of the Fergana depression and the foot of the Alay and Turkestan ridges). The host rocks are represented by alternating grey inequigranular gradational-layered sandstones, gravel, associated with sandstones by gradual transitions, and dark-grey carbonaceous siltstones, enriched in organic matter. Gold mineralization is confined to the main contact of the Tolubai Formation and May limestone. The rocks of the Tolubai Formation and May limestones have undergone pervasive hydrothermal alteration near the "main contact". Based on the study of host rocks, three main types of gold-associated alteration have been recognized, such as jasperoides, decarbonatization, and sulfidization. Mineral composition of the Kadamzhai and Chauvai deposits is similar to gold deposits located in Nevada and Guizhou province. These deposits contain both Au and Sb-Hg. The main minerals in gold ore are pyrite, marcasite, arsenopyrite, orpiment, and realgar. The Sb-Hg ores are represented by cinnabar and stibnite. Deposits contain invisible gold (no observed native gold) associated with arsenic, antimony, mercury, and thallium, and have high gold-silver ratios. The distribution of gold is structurally controlled and is disseminated in the wall rocks. Structural settings for gold mineralization at the Kadamzhai and Chauvai deposits are transpressional regime. Based on geology, geochemical signatures and mineral composition of the Kadamzhai and Chauvai deposits that these deposits can be classified as Carlin type.