Relationship between porphyry tin deposit and ore-bearing subvolcanic rocks:Geochronological evidence from Llallagua tin deposit in Bolivian tin belt
The Bolivian tin belt is one of the most important tin polymetallic metallogenic belts in the world.In this belt,tin ore bodies are mainly hosted in subvolcanic rocks and there is no granite in the tin mining area,which is obviously different from close relationship between tin deposit and granite in other tin deposit globally.The tem-poral relationship between the sub-volcanic rocks and tin deposit still remains unclear.The Llallagua tin deposit,located in middle part of the Bolivian tin belt,is one of the largest tin deposits in the world.Previous studies found that the rhyolite porphyry is much older than tin mineralization,suggesting that tin ore has no temporal and genetic relationship with the ore-hosted subvolcanic rocks.However,the tin ore bodies is mainly hosted in dacite porphyry as veins and the temporal and genetic relationships between the dacite porphyry and tin deposit remain unclear.Base on detailed field geological observation,this study reports the geochronological data of the ore-host-ed dacite porphyry.The LA-ICP-MS U-Pb ages of zircons from two samples of dacite porphyry are(21.8±0.1)Ma and(21.3±0.3)Ma,which is well consistent with the previous reported U-Pb age of monazite(23.4±2.2)Ma and the U-Pb age of cassiterite(24.0±5.1)Ma from the tin veins.It indicates that the tin ore and the ore-bearing subvo-lcanic rocks have a close temporal relationship.Considering that the tin ore bodies are vein-like within the dacite porphyry and the dacite porphyry itself has limited mineralization potential,we think that the dacite porphyry is not the ore-forming rock for tin ore,and we speculate that there are contemporaneous concealed ore-forming rocks for tin ore deep underground associated with the monzogranite.Furthermore,the results of the petrological and metallogenic chronological framework show that the regional porphyry tin deposits and the ore-bearing sub-volcanic rocks were also formed at the same time.Finally the timing of magmatic rocks and tin deposits of the Bolivian tin belt can be divided into two stages:Triassic to Jurassic and Late Oligocene to Miocene.The Triassic to Jurassic tin deposits are mainly distributed in North area of the belt.The Oligocene and Miocene tin deposits are distributed in all belt and became younger from the North to the South.
subvolcanic rocksmetallogenic ageLlallagua tin depositBolivian tin belt
万方数据
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