Mineral Characteristics and Geological Significance of the Longmala Lead-zinc Skarn Deposit,Tibet
The Longmala lead-zinc deposit is a typical skarn-type deposit located in the eastern section of Gangdese-Nyainqengtanglha lead-zinc metallogenic belt.Although the source and evolution of its ore-forming materials,diagenetic and metallogenic ages,and the dynamic background of its formation have been well studied,systematic research on its skarn mineralogy and zonation model is lacking.In this study,detailed field geological cataloging,systematic microscopic identification,and electron probe analysis were used to investigate the mineral association and composition as well as zonation characteristics of this skarn deposit in Tibet.Skarn minerals in the deposit mainly consist of garnet,pyroxene,wollastonite,chlorite,and epidote.The mineral association and chemical composition of the skarn have an obvious zonation in space.The skarn develops mainly in the contact zone between hornstone and marble or fills in the wall rock along cracks,showing transversal characteristics from faded hornstone → garnet skarn → dark hornstone → diopside skarn(ore body)→ marble → hornstone.In the vertical direction from the roof to the floor,the lithological zonation is from hornstone → garnet skarn →diopside skarn → marble → garnet skarn → diopside skarn → hornstone.The garnet in the deposit belongs to the homomorphic series(And7.92～88.63Gro5.92～86.46Pyr+Spe1.04～5.11),with a wide range of end-member components,indicating that the environment in which the skarn formed is not a completely closed system.The garnet in the ore-bearing skarn of the main Pb-Zn ore body shows that the ore-forming fluid migrated from the southwest to the northeast to form the main ore body.These findings provide guidance for future searches for ore-forming rock masses and deep prospecting.
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