《Table 2.Porosity and permeability of parametamorphic rocks in Pingxi area.》

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《"Characteristics of parametamorphic rock reservoirs in Pingxi area, Qaidam Basin, NW China"》

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Core，thin section，scanning electron microscopy and X-ray diffraction analysis confirmed that there are three types of parametamorhpic rock reservoirs in Pingxi area.The first type is the Silurian slate，gray or gray-green，with slab structure and palimpsest texture，possessing residual metamorphic structure，and residual quartz and feldspar in directional arrangement（Fig.2）.The main mineral components are clay and quartz，the two combined account for more than 60%；the calcite accounts for 5%to 16%；the feldspar group accounts for 2%to 3%，largely albite.The other mineral componentsinclude a small amount of pyroxene（mainly from the original rock），anhydrite，barite，and pyrite（Table 1）.The second type is the Ordovician crystalline limestone，with low metamorphism degree and some original rock features.The crystalline limestone is the main rock type in the Pingxi area，gray，grayish white or greenish gray，with massive structure and high content of crystalline calcite in directional arrangement（Fig.2）.The mineral composition is chiefly calcite，accounting for45%to 60%，and the content of dolomite is low；quartz and clay minerals each account for 10%to 25%；the rest are a small amount of albite，siderite，barite and anhydrite（Table 1）.The third type is the Ordovician mica-quartz-bearing calc-schist of dark gray and grayish white with slab structure；in it are some calcite and sericite minerals in directional arrangement.The biotite and calcite have rich cleavages（Fig.2）.Calcite and clay are the major mineral components，combined accounting for 42%to 72%；the second is quartz，accounting for 20%to 40%；the proportion of feldspar is 0.5%to 12.0%，mainly albite.The rest components in small quantity include analcime，barite，and anhydrite（Table 1）.In summary，the three types of parametamorhpic rock reservoirs in Pingxi area can be told from each other clearly.Slab structure is common in slate，cleavage is very developed in calc-schist，and crystalline limestone has non-obvious structure due to high content of crystalline calcite with high plasticity.The distribution of granular and flaky minerals in parametamorhpic rocks has a good correlation with the degree of metamorphism.The calc-schist has the highest metamorphism degree and the highest degree of mineral directional arrangement，crystalline limestone is the second，and slate is the last.