The Comparative Study On Metallogenic Mechanism Of Hard-rock-type Lithium Deposits In Jiajika,Sichuan And Kaluan,Xinjiang

Lithium resource is a key strategic reserve resource,which plays an important role in the fields of national economic construction and defense science and technology,and is known as “the metal to promote the world forward”.Granite pegmatite is the product of the special evolution process of magma,and is also the main source of lithium resources and rare metals at present.However,there are still different views on the genetic relationship between granite and pegmatite.It is mainly lack of in-depth understanding of the magmatic differentiation and evolution process of granite pegmatite,so it is difficult to effectively restrict its metallogenic effect and lithium abnormal enrichment mechanism.On this basis,a comparative study was carried out between the Jiajika deposit in western Sichuan and the Kalu’an lithium deposit in Xinjiang.Through Li isotope and other element geochemical methods,the genetic relationship between granite and pegmatite was deeply explored,and the metallogenic process of granite pegmatite and the main factors promoting lithium enrichment were revealed.At the same time,the similarities and differences between the Jiajika lithium deposit in western Sichuan and the Kalu’an lithium deposit in Xinjiang are summarized,and the lithium formation mechanism of different types of hard-rock-lithium deposits is further explored,which provides certain theoretical guidance for prospecting and exploration.The main findings are:(1)Geological characteristics of the deposit: Jiajika and Kalu’an lithium deposits are highly similar in regional geological background,mineralization types and exposed strata lithology,but they are quite different in mining area structure,metallogenic zoning and granite types.The surrounding rock of pegmatite in the two mining areas is mainly a set of metamorphic sedimentary rock basement,and the ore minerals are mainly spodumene and lithium mica.The formation of lithium deposits is closely related to orogenic activities and thermal history evolution.(2)Petrogeochemical characteristics: The two mica granites in the Jiajika and the biotite granite in the Kalu’an are both high silicon,alkali-rich and peraluminous S-type granites,which are derived from partial melting of metamorphic sedimentary rocks in the mining area,but the evolution degree of the former is slightly higher than that of the latter.The Jiajika pegmatite mainly comes from the crystallization differentiation of mica granite,while the Kalu’an pegmatite mainly comes from the partial melting of metasedimentary rocks.(3)Li isotope characteristics: In the late differentiation stage of the granitic pegmatite magma of Jiajika and Kalu’an,fluid exsolution occurs.In the process of fluid exsolution,Li and other incompatible rare metal elements tend to be enriched in the residual melt,resulting in further enrichment of Li content in pegmatite magma.(4)Source of ore-forming materials: The initial ore-forming materials of the two mining areas are derived from metamorphic sedimentary rocks(hornstone,schist,slate)in the mining area.On the one hand,metamorphic sedimentary rocks provide a place for migration and precipitation for mineralization.On the other hand,the metamorphism of mudstone and sandstone realizes the first enrichment of lithium ore,and provides a material basis for mineralization.(5)Characteristics of ore-forming fluids: The ore-forming fluids of Jiajika and Kalu’an pegmatite show mixed characteristics of crust-derived fluid,mantle-derived fluid and saturated atmospheric water.The main source fluid is crust-derived fluid,and the contribution of mantle-derived fluid is relatively small.With the progress of mineralization from spodumene-barren pegmatites to spodumene-bearing pegmatites,crust-derived fluid and atmospheric precipitation have increased.(6)The formation mechanism of the deposit: the spodumene-bearing pegmatites in Kalu’an is mainly derived from the partial melting of Li-rich metamorphic sedimentary rocks(hornfels,schist,slate),which realizes the enrichment from the initial deposition,the first enrichment of thermal metamorphism to the second enrichment of pegmatitization;the metallogenic process of the Jiajika lithium deposit includes the initial enrichment of deposition,the first enrichment of thermal metamorphism,the second enrichment of granite and the third enrichment of pegmatitization.There is a great difference in the lithium formation mechanism between the two deposits.(7)Prospecting and exploration guidance: Summarize the characteristics of lithium mineralization in the two regions,and advocate searching for highly differentiated granite and pegmatite veins in the secondary fractures of metamorphic dome structure in the Jiajika area.Albite and muscovitization are delineated in pegmatite veins,because ore-bearing pegmatite veins are closely related to albite and muscovitization.In Kalu’an area,it is advocated to search for pegmatite veins at the intersection of tectonic fissures in biotite quartz schist strata.Lithium deposits mostly occur in the center of the expanded pegmatite rock mass at the intersection of fissures.