A study on A-type granites in Suzhou, China
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The Suzhou granite suite is the anorogenic product, which is located on the inactive continental margin of east China. It was emplaced about 141 Ma ago, occurring as a stock with a polygonal outline on the surface, belonging to alkali potash-feldspar granites with K2O > Na2O, Reit’s alkali coefficient = 0.694, SiO2 = 74.95, and Al2O3/(K2O + Na2O)mol= 1. Besides K and Na, Li and Rb are also rather high. Highlycharged metals such as Zr, Nb, REE, Y, Sn, Th, Ga and Zn are 10, or even 50 times higher than those in the ordinary granites. Halogen elements such as F and Cl are high in abundance with F = 2700 ppm and Cl = 170 ppm on average. The abundances of deep-source elements such as Ti, Al, Ca, Mg and P are relatively low, with A12O3 = 12.65% and Ca + Mg < 1%. High Ga and low Al contents are typomorphically characteristic of A type granites.
Biotite in the rocks is, for the most part, annite, usually filling in quartz and feldspar crystals, indicating that the crystallization of magma proceeded under relatively anhydrous condition.
More than 40 kinds of accessory minerals have been identified, of which the mantle-derived mineral chrompicotite and moissanite is of great interest.
Two different intrusions, the major and supplementary intrusions, can be distinguished in the granite suite. The rock-forming temperature is estimated to be 810°C, pressure 2.5 kbars, pH 8.1,18O/16O low(δ18OWR = 6.19‰), andfo2= 10−16. The abundances of REE are high and Eu depletion is remarkable (δEu = 0.24).
A variety of mineral deposits related to the Suzhou granite suite have been recognized.
KeywordsPrimary Facies Accessory Mineral Basic Magma Potash Feldspar Granite Suite
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