Mineral composition and brittle mineral contents of organic-rich mudstone are critical to fracturing

so they are important parts of shale gas reservoir description and evaluation.X-ray diffraction and microscopic observation were performed on outcrop samples from organic-rich mudstones in the Silurian Longmaxi Formation in the Upper Yangtze region.The results show that the contents of brittle minerals average about 50-70%.The clastic minerals of organic-rich mudstones mainly consist of quartz

few feldspars and very few detritus in the lower Longmaxi Formation of the Silurian on Wangcang

Leibo and Xishui outcrops.The clastic mi-nerals have clear angular shape and scattered distribution and no clear orientation.Authigenic brittle minerals are mainly calcites and dolomites.Calcites and dolomites show semi-euhedral to euhedral crystalline

relatively rich in local strata forming slight fringes.Pyrites are common but its content is low.Biogenic minerals are rare and mainly of siliceous radiolarians with the characteristic of dissolution.Regionally

brittle mineral combinations can be divided into two types:quartzs-feldspars and quartzs-feldspars-calcites-dolomites.High calcite and dolomite contents occur in main sedimentary centers

i.e.Luzhou-Yibin area in Sichuan

Wulong-Shizhu area in Chongqing and the northern margin of Central-Guizhou-Xuefeng uplift.Hannan ancient land and Central Sichuan uplift are different from Central Guizhou-Xuefeng uplift in the capability of providing detrital sediments

resulting in different mineral composition in the marginal shallow water deposits.In summary

the key to find brittle-mineral rich areas is the reconstruction of palaeogeography

especially the analysis of sedimentary microfacies.