Yongfeng composite granitic pluton, Xingguo Co., Ganzhou, Jiangxi, Chinai

Regional Level Types
Yongfeng composite granitic pluton	Pluton
Xingguo Co.	County
Ganzhou	Prefecture
Jiangxi	Province
China	Country

The Yongfeng composite granitic pluton consists of Yongfeng, medium- to coarse-grained biotite porphyritic monzonite granite and Longshi fine-grained biotite monzonite granite, with an outcrop area of 350 km2. The northern, eastern, and western parts of the composite granitic pluton are in contact with epimetamorphic rocks of the Laohutang formation and Bali formation, and the southern part intrudes the Qingxi granite. The Yongfeng granite occurs along the margins of the composite granitic pluton, predominantly composed of reddish or grayish white medium–coarse grained porphyritic biotite monzonitic granite, occasionally with potash feldspar phenocrysts. The main minerals are alkali feldspar, plagioclase, and quartz, with a small amount of biotite and muscovite, and the accessory minerals are zircon, apatite, monazite, and rutile. Alkaline feldspar mainly consists of microcline and perthite, with a semi-idiomorphic plate shape. The length ranges from 0.2 mm to 8.0 mm, with a content of 35 vol%. Tartan twinning and striped structure can be observed. Plagioclase occurs in the form of semi-idiomorphic plate, and polysynthetic twin can be observed, with a length of 0.2–7.0 mm and a content of 32 vol%. The alkali feldspar and plagioclase have undergone strong sericitization alteration. Quartz has a xenomorphic-granular shape, with a diameter of 0.2–5.0 mm and a content of 30 vol%. In the hand specimen, biotite appears as a clump-like aggregate, and under the microscope, it appears scaly, with a length of 0.2–10 mm and a content of 2 vol%. Muscovite also appears scaly (Figure 3a,d), with a length of 0.2–0.6 mm and a content of 1 vol%. The biotite and muscovite have undergone strong chloritization alteration. The Longshi granite is located in the middle of the composite granitic pluton and intrudes the Yongfeng granite. The edges of the granite are heavily weathered. The lithology of the Longshi granite is similar to that of the Yongfeng granite, with only differences in mineral grain size, content, and the phenocrysts content. The lithology of the Longshi pluton is fine-grained biotite monzonitic granite, occasionally with feldspar phenocrysts. The main minerals include potassium feldspar (~20 vol%), plagioclase feldspar (~30 vol%), and quartz (~40 vol%), followed by biotite (~8 vol%) and muscovite (~2 vol%). Potassium feldspar occurs in semi-idiomorphic plate form with grain sizes of 0.2–1.5 mm, with occasional occurrences of striped feldspar and microcline. Plagioclase feldspar occurs in semi-idiomorphic plate form with grain sizes of 0.2–2.0 mm, showing the development of polysynthetic twins. Quartz occurs in granular form with grain sizes of 0.1–2.5 mm. Biotite occurs in scaly form, with a length of 0.1–1 mm. Muscovite occurs in scaly shape, with a length of 0.1–0.6 mm. The accessory minerals mainly include apatite, xenotime, zircon, and a small amount of metallic minerals. The alteration mainly includes K-feldsparization, silicification, sericitization, chloritization, epidotization, and carbonatization.

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