SALTNESS AND GEOLOGIC BACKGROUND OF THE CAMBRIAN STRATA IN THE SICHUAN BASIN IN THE UPPER YANGTZE AREA

As a matter of record,little research was made on the Cambrian gypsoliths in the Upper Yangtze area.A wide range of evaporites such as corroded breccia,anhydrite,halite and K-rich brines have now been noticed in this area.Sedimentary facies have experienced the evolutionary stages from the basin facies through platform facies to evaporite facies.The regressive sedimentary sequences have been found in the Middle and Lower Cambrian strata.The palaeotectonic and palaeogeographic settings are believed to be the important ore-controlling conditions.The movement of the peripheral plates and folding of the plastec basement resulted in the formation of the periplat-formal upliftS and intraplatformal depressions.The sedimentary facies and palaeogeographic maps display a pattern of sedimentary facies belts as the "tear-drop pattern" ranging from carbonates through sulfates to chlorides.The evaporites rest on the periplatformal uplifts,and the reef growth has graded into the barrier lagoon to saline lake stages.
The evaporite series are developed in the sedimentary basins in steadily subsiding area,with thicker halite rocks whose Br/Cl ratios range between 0.2 and 0.4.The palaeoclimates are dry and hot.The sedimentary(confined)water and leach water occur around the evaporite rock bodies, with K(K⁺)contents varying between 0.1 and 4.76g/1.The hydrologic-geochemical values(such as K/Cl ratios,sylvite ratios and K/Br ratios)indicate a normal K content.The concentrated brines in the saline lakes reach the depositional stages of the chlorides.There exist the corresponding tec-tonically enclosed conditions.The salt-bearing geological indicators occur on a wide range of scales. It is concluded that there may be the mineralization conditions for potassic salts in the study area. However the target strata are buried too deeply,and therefore the effective metallogenic prognosis should be made in the shallower depths.