Textural zonation of pegmatites and multiple-phase magmatic mineralization in the Jiajika lithium deposit in western Sichuan
LCT(lithium-cesium-tantalum)pegmatites exhibit two types of zonation:internal and regional.Internal zonation refers to the compositional zoning within a single,typically voluminous pegmatite vein.Different rare metal mineralizations can develop within distinct textural zones of a single vein,as exemplified by the Koktokay No.3 pegmatite in Xinjiang.Regional zonation,on the other hand,describes the distribution of pegmatite and ore-forming systems around a central,highly differentiated peraluminous granite body.Hundreds of pegmatite veins surrounding the granite show varying pegmatite types and mineralization types.Pegmatite evolution increases with increasing distance from the granite center.Consequently,single veins of such pegmatite in the regional zonation are smaller,exhibit less pronounced zonation,and possess different ore-bearing properties.The Jiajika lithium deposit is a typical representative example of this kind of pegmatite deposit.Field investigations at the Jiajika mining area show variations in internal zonation among pegmatite veins.Veins No.9(Be-bearing),No.133(Li-bearing),and No.528(Nb-Ta-bearing)display well-developed internal zonation patterns.In contrast,veins No.104 and No.308(both Li-bearing)exhibit less pronounced internal zonation,potentially due to multiple phases of magmatic-hydrothermal activity.The interpenetration of pegmatite veins in the Jiajika mining area suggests multiple phases of magmatic and metallogenic processes.Scientific drilling(JSD-2 and JSD-3 boreholes)confirmed this byencountering spodumene-bearing pegmatite and aplite veins intruding into the barren Majingzi granite.Mineral dating within the pegmatite indicates at least two stages of pegmatite formation:213～206 Ma and 199～191 Ma.Borehole JSD-1 data suggests a progressive evolution of magma from deep to shallow levels,with increasing differentiation.Granite and pegmatite compositions evolve synchronously from bottom to top.The granite sequence transitions from biotite granite to muscovite-bearing biotite granite,two-mica granite,muscovite granite,and finally albite granite.Similarly,the pegmatite sequence progresses from microcline type to microcline-albite type,albite type,and ultimately albite-spodumene type.According to the mineralization characteristics of the pegmatite at different depths,the vertical zonation of the Jiajika deposit can be roughly divided as follows:a Li-Be-Nb-Ta mineralization zone(0～105 m);a Be-Nb-Ta mineralization zone(0～860 m);a first phase Nb-Ta mineralization zone(0～1730 m);a barren pegmatite zone(1730～3170 m);and a second phase Nb-Ta mineralization zone(3170～3211)m.
万方数据
维普
