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The Uragen giant sandstone-hosted Zn–Pb deposit has a proven reserve of 5.90 Mt metals in the southern ore zone and potentially 10 Mt metals for the whole deposit, and orebodies are strictly confined to the bleached clastic rocks of the Lower Cretaceous red beds. The bleaching has been used to guide lead–zinc exploration; however, its nature and origin, as well as the relationship with Zn–Pb mineralization, remains unclear, although it is closely related to regional oil–gas infillings. Detailed field investigation and petrographic observation, TESCAN-integrated mineral analyzer (TIMA), and X-ray fluorescence (μ-XRF) analysis of the red and bleached sandstone at the same sedimentary layer demonstrate that the bleaching is mainly caused by the reductive dissolution of hematite pigment, which probably resulted from the interaction with H2S formed by in situ sulfate reduction during hydrocarbon migration. The calcite cements in the bleached sandstones show δ13C and δ18O values of −5.36~−5.94‰ and 20.94~27.91‰, respectively, and these samples fall close to the evolution line of decarboxylation of organic matter in δ13C-δ18O diagram, also suggesting a genetic relationship between the bleaching and hydrocarbon-bearing fluids. Petrol–mineral composition changes and sulfide characteristics of red, bleached, mineralized zones, as well as pyrite locally replaced by coarse-grained galena in the mineralized zone, imply that the bleaching may occurred before Zn–Pb mineralization. Mass balance calculation and μ-XRF analysis indicate that large amounts of Fe and minor Zn were extracted from red beds with little or no sulfates; however, the red beds with abundant sulfates may be a sink for leached ore metals during the bleaching process. We therefore propose that the former accumulations of iron sulfides and reduced sulfur in the bleached zones may provide an ideal chemical trap for later Zn–Pb mineralization, and the bleached zones with high ∑S contents are the favorable prospective targets of the Uragen-style sandstone-hosted Zn–Pb deposits. [ABSTRACT FROM AUTHOR]

The Ulugqat Basin is located at the juncture of the Tarim Basin, the western Tianshan Orogen of the Central Asian Orogenic Belt, and the Pamir salient of the Tethys domain. A comprehensive provenance study using sedimentology, petrology, and detrital zircon U–Pb geochronology was carried out on the clastic rocks of the fifth member of the Lower Cretaceous Kezilesu Group from the Ulugqat Basin, aiming to better understand the nature of its relationships with the neighbouring tectonic units as well as the formation of sandstone‐hosted Zn–Pb mineralization. The fifth member consists of conglomerate, gravelly sandstone, sandstone, and mudstone interbeds, and is interpreted as alluvial fan–braid river–braid river delta sediments. The conglomerate and gravelly sandstone contain different kinds of lithic fragments, including phyllite, quartzite, chert, chalcedony, and some felsic igneous rocks, with low compositional maturities. The detrital zircon U–Pb ages of sandstone from the uppermost part of the fifth member range widely from 229.7 to 2,984.9 Ma, concentratedly distributed in five groups: 230–300, 390–480, 750–880, 1,600–2,200, and 2,300–3,000 Ma. The identified palaeocurrent directions, heavy mineral assemblages, specific provenance indicators, and distributions of detrital zircon U–Pb ages all indicate that these clastic rocks are probably sourced from the South Tianshan Orogen to the north, rather than the Pamir salient, probably involving the Proterozoic Aksu metamorphic rocks, Palaeozoic sedimentary rocks, Late Carboniferous–Early Permian alkali granite, and some mafic/ultramafic rocks of ophiolitic mélange. This interpretation is consistent with a late Early Cretaceous uplifting of the South Tianshan Orogen according to previous low‐temperature thermochronological data sets. The thick deposition of these Lower Cretaceous clastic rocks and associated uplifting of the South Tianshan Orogen are interpreted to be related to the coeval collision of the Karakoram–Lhasa Block with the southern Asian margin. [ABSTRACT FROM AUTHOR]