Pegmatite-type mineralization of rare metals in the Altai orogenic belt,Xinjiang
Granitic pegmatites are intimately associated with rare-metal mineralization(e.g.,Li,Be,Nb,and Ta).Despite extensive research and discussion surrounding the metallogenic model of pegmatites and their genetic relationship with granites,certain controversies remain unresolved.The Altai orogenic belt in northern Xinjiang,renowned for its abundance of well-studied pegmatite-type rare-metal deposits,provides a valuable case study for addressing these complexities.This paper presents a systematic synthesis of the geological background and metallogenic characteristics of the Altai pegmatites.We delineate three distinct genetic relationships between pegmatites and granites in the Altai orogenic belt:①Pegmatites derived from independent pegmatitic melts via anataxis,showing no genetic connection with granites;② Pegmatites exhibiting coeval and proximal origins with granite,suggesting a shared magmatic ancestry;③ Pegmatites that represent derivative products of parental granitic magmas,both components integrated within a granite-pegmatite magmatic system.Meanwhile,we propose a petrogenetic-metallogenic model for the pegmatite in the region and speculate that pegmatites of different genetic styles may coexist at provincial,orefield,and deposit scales.The formation of the Altai pegmatite-type rare metal province was influenced by the presence of Paleozoic sedimentary rocks.In addition,the Altai orogenic belt,located in a mantle slope zone,exhibits susceptibility to far-field impacts from external tectonic events.In the Triassic,the formation of rare metal-bearing pegmatites was triggered by the far-field impact of the northward-directed accretion of terranes formerly associated with the Gondwana Land(Tethys tectonic domain)onto the southern margin of Eurasia.In the Jurassic,the tectonic framework,petrogenesis,and mineralization in the Chinese Altai were collectively influenced by the far-field effects of the Neo-Tethys and the Mongolia-Okhotsk Ocean tectonic events.
rare metalspegmatitegraniteAltai orogenic belttectonic model of pegmatite genesis and mineralizationfar-field impact
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