Study of diagenetic and hydrothermal alteration in stratigraphy section of Momen-abad (North- East of Sarbisheh ,Birjand) and its role of them in non-metallic mineralization

Momen-abadarea is located in the south of Birjand and northeast of Sarbishe. By considering four stratigraphy section in Momenabad bentonite mine, the area has been studied in terms of diagenetic and hydrothermal alteration. In each of the four sections, diagenetic alteration has been observed on volcanic pyroclasts from acidic to intermediate rock types; such as, rhyolite, dacit, andesite and pyroclastics from tuffs to ignemberits. Moreover, according to the structure of the area in terms of tectonic and existence of fractures and faults in the area, and fragments of volcanic members, it seems that, they are the origins of effective fluids on magmatic alteration. Also, they have ascended through fractures and faults. Besides, they have caused multiple alteration in pyroclastics of the area. Predominant alteration of these pyroclastics are types of intermediate to advance argillic, silicization, chloritic and sericitic. Silicified alteration is the indicator of acidic hydrothermal environmentand fluids, and it has a lot of silica in itself. This alteration in dacitic rocks has been demonstrated in forms of quartz in vein and spherulitic which have filled vesicoles. Sericitification has been produced by alteration of plagioclase and alkali feldspar, and existence of fluids which have been enriched from water and k+. Chloritization has been produced from alteration of clinopyroxene and plagioclase, and with entrance of hydrothermal fluids in to the andesite rocks. According to XRD studies which have been carried out formation of bentonite caused by alteration, and montmorillonite type is predominant in the main mine section(section 4), and tuff and ignimbrite (section 2) in the area.