Beiyingxigou Pb–Zn–Ag deposit, Pingshan Co., Shijiazhuang, Hebei, Chinai

Regional Level Types
Beiyingxigou Pb–Zn–Ag deposit	Deposit
Pingshan Co.	County
Shijiazhuang	Prefecture-level City
Hebei	Province
China	Country

The Beiyingxigou Pb–Zn–Ag deposit shows a dominant structural control by N–S and N–W trending faults. The Precambrian metamorphic rocks which constitute the basement in the area are characterized by gray gneisses intercalated with plagioclase amphibolite and dolomite marble, K-feldspar leptite, and felsic granulites. Voluminous intermediate-felsic intrusions of Yanshanian were emplaced at around 130 Ma, and are exposed in the Beizhuang, Guanyingtang and Houdouling areas. These rocks are mainly composed of medium to fine-grained diorite, quartz monzodiorite, quartz monzonite, monzo-granite, and porphyritic monzogranite. The main Mapeng granitoid pluton is exposed around an area of 64.5 km2, and is composed of porphyritic monzogranite, coarse grained granodiorite, and medium- to fine-grained quartz–monzodiorite from the inner to outer zones. The intermediate-acid dikes trend NNE and NNW are mainly composed of granite porphyry and granodiorite- porphyry which intrude the Precambrian basement. Around 26 Pb–Zn–Ag-bearing altered fracture zones hosted in biotite plagioclase gneiss and biotite monzo-gneiss have been identified in this ore deposit, mostly controlled by N–W trending faults. Among these, two ore bodies have been delineated so far from the altered zones separately named as Sb1 and Sb2. The mineralized fracture zone hosting Sb1 ore body is about 3000 m in length and 3–20 m wide, trending NNW, with steep dips (75°–85°) towards SW. The Sb2 ore body is located about 1.6 km northeast of Sb1 and runs parallel to Sb1. The mineralized fracture zone is about 2200 m in length and 5–30 m wide, with southwestwards dip at steep angles of 75°–85°, similar to Sb1. Both the Sb1 ore body and the Sb2 ore body are characterized by much more quartz veins or veinlets compared with the barren alteration rocks.
Based on the ore textures, structures and the observed mineral assemblages, we identify two periods of ore formation: a hydrothermal period and a supergene period. Among these, the hydrothermal period is the predominant and includes 4 stages as follows. (1) Pyrite phyllic stage, where cubic pyrite crystals of about 1–2 mm grain-size are sparsely disseminated within aggregates of milky quartz and scaly sericite of b0.5 mm size imparting a yellow-green hue. (2) Quartz–pyrite stage which is divided into pyrite–quartz and quartz–pyrite sub-stages based on the contents of pyrite and quartz. In the pyrite–quartz sub-stage, fine grained milky quartz aggregates constitute about 80% volume, and medium-fine grained pyrite is distributed as disseminations. In the quartz–pyrite sub-stage, coarse grained pyrites are distributed as dense disseminations (40–50% volume), with the gray white quartz constituting about 20%. These two sub-stages show a gradational change that sometimes cannot be distinguished clearly. (3) Quartz –polymetallic sulfide stage represented by fine- or coarse-grained galena and gray quartz that show veined, dense dissemination or mottled distribution, followed by fine-grained sphalerite and chalcopyrite distributed as sparse disseminations (4) Quartz–carbonate stage, where later formed quartz–calcite stringer veins are interwoven with the early ore assemblages. Among the various stages above, the quartz–polymetallic sulfide stage is the main ore-forming stage.

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References