Geology,Geochemistry and Genesis of Yinyan Porphyry Tin Deposit

The Yinyan porphyry tin deposit is a blind deposit associated with a small granite porphyry stock.The petrology and geochemistry of the Yinyan granite porphyry suggest that it is genetically of the transfor-mation type,emplaced at the late stage of fractional crystallization within a high-level magma chamber.Ore-forming fluids are derived predominantly from the granitic magma and they interact with the wall rocks intensely when finding their way upwards through the granite porphyry.From the lower part of the porphyry upwards the following alteration zones can be distinguished(a)slightly altered granite porphyry (with weak potash feldspathization),(b)protolithionite-quartz greisenization zone,(c)to-paz-quartz greisenization zone,(d)senicite-quartz sericitization zone,and （e）silicification zone (quartz core at the surface).Tin mineralization is related to greisenization,especially to topaz-quartz greisenization.Rock and ore-forming temperatures and oxygen fugacities are estimated,respectively.There are significant differences in many aspects between the Yinyan porphyry tin deposit and volcan-ic-subvolcanic porphyry tin deposits.

Geology,geochemistry and genesis of Yinyan porphyry tin deposit

The Yinyan porphyry tin deposit is a blind deposit associated with a small granite porphyry stock. The petrology and geochemistry of the Yinyan granite porphyry suggest that it is genetically of the transformation type, emplaced at the late stage of fractional crystallization within a high-level magma chamber. Ore-forming fluids are derived predominantly from the granitic magma and they interact with the wall rocks intensely when finding their way upwards through the granite porphyry. From the lower part of the porphyry upwards the following alteration zones can be distinguished: (a) slightly altered granite porphyry (with weak potash feldspathization), (b) protolithionite-quartz greisenization zone, (c) topaz-quartz greisenization zone, (d) sericite-quartz sericitization zone, and (e) silicification zone (quartz core at the surface). Tin mineralization is related to greisenization, especially to topaz-quartz greisenization. Rock- and ore-forming temperatures and oxygen fugacities are estimated, respectively. There are significant differences in many aspects between the Yinyan porphyry tin deposit and volcanic-subvolcanic porphyry tin deposits.