论我国沉积改造金属矿床

A DISCUSSION ON SEDIMENTARY REFORMED METALLIC DEPOSITS IN CHINA

在论述沉积改造金属矿床Ｈｇ、Ｐｂ、Ｚｎ、Ｓｂ和菱铁矿的成矿、改造机理及赋存深度的基础上，作者认为沉积改造金属矿床是先沉积后成矿或改造的，成因清楚，含义明确，应从“层控矿床”中划分出来，单独成为一类矿床类型。该矿床赋存深度在潜水面以下２００～３００ｍ或４００～５００ｍ以内、地下水滞流带以上“还原成矿改造带”

The sedimentary reformed metallic deposits in China, such as mercury, lead, zinc, antimony and sedimentary reformed siderite deposits, were usually considered to be of mesothermal epithermal type Nevertheless, as isotopic compositions of fluids in mineral inclusions indicate meteoric water with metallogenic and reformation temperature lower than 250℃, these deposits should belong to sedimentary reformed metallic deposits At the first stage, mercury, lead, zinc and antimony were scattered in wall rocks, with no economic value; the originally deposited massive lean siderite ore beds were low in iron grade With the thickening of overlying strata, these ore materials gradually got buried at the great depths of several hundred to several thousand meters With the uplifting of the earth crust, the scattered metallic compounds or lean siderite ore beds (with abundant silica) ascended to the reducing metallogenic reformation belt within 200￣300 m below the groundwater table, where physical chemical conditions changed (Eh=0￣-0 7 mV, pH=5￣6 or 7￣8), and both alkaline conditions for reduction and metaacid conditions for reduction existed Under the reducing alkaline conditions, mercury, lead, zinc and antimony were dissolved into transportable metallic sulfur hydrogen complexes such as HS -; under reducing metaacid and favorable lithologic as well as structural conditions, ore forming materials might be concentrated to form economically valuable ore deposits of such metallic sulfides as cinnabar, galena, sphalerite and stibnite Siderite might also be reformed and crystallized into rich siderite ore within 200￣300 m beneath the groundwater table Modern groundwater table is not concordant with the paleogroundwater table during the mineralization and reformation, which might be within 200￣300 m or 400￣500 m below the lowest regional base level of erosion of the ore district