Metamorphosed Overprints And Prospecting Evaluation On The VMS Deposits In The Kelan Basin, Altay

The VMS deposits in Kelan volcanic-sedimentary basin of Southern Altay, formed in the Early-Middle Devonian, was subjected to intense deformation and metamorphism in the orogenic setting since Late Devonian. However, the studies about deformation, metamorphism and superimposed mineralization in relation to VMS deposits are less constrained. In this paper, based on new field and laboratory researches on deposit geology, ore-forming fluids and geochemical characteristics in the Talate and Tiemurte Pb-Zn deposits, we present new insights of the ore genesis. In addition, the metallogenic model and ore prospecting are constructed in the end.The Talate and Tiemurte are the representative marine volcanic-sedimentary Pb-Zn deposits in the Kelan Basin, hosted in the metamorphic rock series of the lower Devonian Kangbutiebao formation. The mineralization is divided into two periods i.e., the submarine volcanic sedimentary exhalation period and the metamorphic hydrothermal overprinting period. The intense metamorphism had occurred in the Talate and Tiemurte Pb-Zn deposits in the Altay orogeny since Late Devonian, resulting in various deformations of the banded and laminated ores and wall rocks.In the Talate Pb-Zn deposit, the primary CO₂-H₂O inclusions in early quartz ?Q1? and late quartz veins ?Q2? have Th,,ot of 294?368? and 142?360 ?, respectively, with the minimum trapping pressures of 100-370 MPa. The CO₂-rich inclusions in the Tiemurte Pb-Zn deposit have Th,tot of 180?³⁴2 ?,with trapping pressures of 100?350 MPa, which suggest that the gold mineralization was derived from metamorphic fluid. The P-T trapping conditions of CO₂-rich fluids are consistent with those of late or post regional metamorphism.The ?⁶⁵Cu of the gold-bearing chalcopyrite from Tiemurte Pb-Zn deposit and Sarekuobu gold deposit suggest that the gold mineralization in the Tiemurte Pb-Zn deposit has the similar origin with Sarekuobu orogenic gold deposit. The ?66Zn of the sphalerite from marine volcanic-sedimentary deposits in the Kelan Basin indicate that the Pb-Zn deposits belong to VMS deposit. The Rb-Sr dating of sphalerite implys that the marine volcanic-sedimentary Pb-Zn deposits in the Kelan Basin formed in Early Devonian ?392±92 Ma?, while the Rb-Sr isotopic age of pyrite and chalcopyrite from Sarekuobu gold deposit suggest that orogenic metamorphism occurred in the Late Permian to Triassic.The sulfur (?³⁴S=-26.46‰?+4‰) was mainly derived from inorganic reduction of sulfates and bacteria sulfate reduction in seawater. The Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb=16.86?18.073,²⁰⁷Pb/²⁰⁴Pb= 15.42-15.623, ²⁰⁸pb/²⁰⁴pb=37.27?38.097) indicate that the homogeneous Pb isotopes from sulfide are possible from the mixing of mantle material and surrounding rocks.The systematical studies show that the extensional basins after island arc along the southern margin of Altay Mountains might result from the subduction of the Erqis ancient Asia oceanic crust in Early Devonian, and then a number of marine volcanic-sedimentary Pb-Zn deposits formed from submarine exhalative-sedimentation. The orogeny of arc-continental collision in the Altay induced extensive deformation and metamorphism from Early Devonian to late Early Triassic, resulting in intense metal reworking and enrichment of early-forming VMS Pb-Zn deposits. The metamorphic fluids continuously extracted the Au from the volcanic stratigraphy with high value of Au, and gold was precipitated in the favorable places, i.e., Sarekuobu and Tiemurte.Based on study, the Pb-Zn deposits in the Kelan basin have further prospecting potential both in the length and depth of ore bodies. Moreover, Au ?Cu? mineralization might be found in the sulfide-quartz veins due to intensive deformation and metamorphism.