| The Xinjiang Sawuer area is located in China in the central part of the CentralAsian Orogenic Belt (CAOB), and previous geological research and exploration ofthis area is minor. There are several world class large and super-large porphyrydeposits in adjacent Kazakhstan, however to date porphyry deposits have not beenreported in the Sawuer district. The only reported deposit, Kuoerzhenkuola, is claimedto be epithermal, based on previous studies, however, its geological characteristicsdiffer from typical epithermal deposits. Consequently there was need to clarify thegeological characteristics and ore genesis of Kuoerzhenkuola deposit. This paperfocuses on Kuoerzhenkuola deposit; it summarizes previous studies, and uses detailedgeological investigations, including petrography, geochemistry, geochronology andshort wavelength infrared spectroscopy to clarify the geological characteristics andore genesis of the deposit, and establishes a new exploration method. The results ofthis work are significant for understanding the regional metallogeny and fordetermining future exploration directions.Our research on the geological characteristics of Kuoerzhenkula deposit indicatesthat it is related to a porphyry deposit. The ore host-rock is diorite. The textures andstructures of the host-rock are dominated by veinlets, disseminations and veins. Fromdeep to shallow, it shows a progression of porphyry alteration types; potassic,propylitic, quartz-sericite (phyllic), clay (argillic), and late calcite alteration. Thesequence of mineral deposition and ore-formation is divided into three stages:potassium silicate stage, quartz sulfide stage and quartz carbonate stage.Analysis by zircon U-Pb LA-ICP-MS shows that the diorite has a concordant U-Pbage of346.6±2.9Ma, and the adjacent andesite crystallized at339.4±4.8Ma,indicating that all formed in the early Carboniferous.Study of major and trace elements shows that host diorite compositions span fieldsbelonging to the calk-alkaline and high-K calk-alkaline series, and are enriched inlarge ion lithophile elements (such as K, Rb, Sr, Ba and Th) and depleted in high fieldstrength elements (such as Nb, Ta). The REE pattern of the diorite is characterized byLREE enrichment, and δEu values are weakly positive. These features arecharacteristic of igneous rocks in an island-arc environment. The parent magma forthese rocks was possibly generated by partial melting of a metasomatized mantle source modified by subducted slab-derived fluids. During its ascent, the magmaexperienced fractional crystallization of ilmenite, apatite, hornblende, pyroxene,sphene and other minerals, and it also experienced crustal contamination.Based on these results, and comparing Kuoerzhenkuola with typical porphyrydeposits, we discuss the genesis of the deposit, and propose a metallogenic model.The model shows that Kuoerzhenkuola is a porphyry Cu-Au deposit, formed in anisland-arc setting associated with subduction of an oceanic ridge in the earlyCarboniferous.Study of short wavelength infrared spectra of altered samples at Kuoerzhenkuolareveals that illite crystallinity is higher and reflectance of the illite absorption peak islower in samples close to the ore body, and the former gradually decreases and thelatter increases in samples away from the ore body. This observation provides a newand easily-applied prospecting criterion for exploration. |
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