| Abstract:The Zhongtiaoshan copper ore district lies along the southern margin of North China Platform,and the Hu-Bi type stratabound copper deposits occur mainly within the black shale of Bizigou Formation in epimetamorphic sequence of Middle Proterozoie Zhongtiao Group, confined strictly to certain stratigraphic horizons. Except for a little basic rock, the Zhongtiao group consists mainly of a suite of sedimentary formation. Breccias are extremely developed in this area and, mainly in the layered form, show gradual facies change with the other sedimentary strata and close spatial association with orebodies. In accordance with their modes of occurrence, two horizons of breccias can be distinguished: one is breccia underlying and making up the lying wall of the orebody, which is restricted to Laobaotan-Diantou district, with relatively large exposed area but basically containing no ore; the other is breccia within the ore-bearing horizon which is extensively distributed, but is relatively small in size and has rich mineralizations. These breccias have extremely poor sorting indices and psephicity, and the composition of the breccias is mainly the same as that of the underlying or neighboring strata. The breccia in the lying wall consists chiefly of marble, argillaceous schist and quartzite, while that in ore layer comprises mainly marble, black schist, quartzite and a few ores. The cemerits are largely composed of dolomite, biotite, quartz, tourmaline, albite, sulfides and a little apatite and seem to have the same mineral assemblage with the host rocks. Textures of hydrothermal activities are ubiquitous in the cements, such as the sieve texture formed by tourmaline enclosed in quartz, and the pilotaxitic peritectio texture fromed by carbonates, quartz and sulfides enclosed in biotite. The tourmaline in the cements is obviously different from that related to granites in composition, but is consistent with the tourmaline from ore deposits of exhalative-sedimentary origin in other areas of the world. It is therefore concluded that breccias in this area&re hydrothermal-sedimentary ones related to submarine hydrothermal exhalative explosion. |
