Preliminary Isotope Studies of the Lianhuashan Tungsten Ore Deposit

Lianhuashan deposit, the first porphyry-type tungsten deposit ever discovered in China, is located in the east of Guangdong Province. Stratigraphically only Jurassic Xiaoping coal series and acidic volcanic rocks occur in the mining area with the latter unconformably overlying the former. Biotite granite, quartz-porphyry and quartz diorite-porphyrite constitute the major intrusives. Rb-Sr isochron ages of the volcanic rocks and the granite are 135.8 ±2.5 m. y. and 137.2± 2.5 m.y. respectively, indicating that they are products of the identical magmatic activity. K-Ar apparent ages vary between 76.6 m.y. and 119.5 m.y. with the K~(40)-Ar~(40) isochron age of volcanic rocks determined at 120.4±12.1 m.y. These ages are as a rule younger than the corresponding Rb-Sr ages. The formation of ferberite-bearing greisen represents the first stage of tungsten mineralization. The K-Ar age of its muscovite is 119.5 m.y., denoting the coincidence of the tungsten mineralization with the igneous rocks in their formation time. The younger K-Ar apparent ages of samples from this area might be chiefly attributed to the effect of the late stage thermal events in the mega-metallogenic belt around the Pacific Ocean. The stable isotope measurements give the following δS~(34)(‰) values:pyrrhotite, from -0.05 to + 3.14;pyrite, from -0.85 to + 3.3; total sulfur(δS_(ΣS)~(34)), 2.0, suggesting that sulfur in the deposits came from deep sources. Initial ratios of Sr isotopes for volcanic rocks and granitic rocks are 0.7061 ±0.0004 and 0.7069 ±0.006 respectively, showing that, in addition of occurring in the same period, they were derived from the same sources. The materials for igneous rocks and tungsten deposits were probably formed as a result of the melting of the oceanic plate along the subduction zone.

 

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