Ore-Forming Fluid Evolution of Shallow Polyhalite Deposits in the Kunteyi Playa in the North Qaidam Basin

Polyhalite occurrence in the Kunteyi Playa in the Qaidam Basin has been known for many years. However, the genetic mechanism of this deposit remains unclear. In this study, a typical section in the playa depocenter is selected to study the polyhalite mineralogy combined with the homogenization temperature and composition of halite fluid inclusions in shallow evaporitic strata. The results show that 1) the main evaporite minerals in the strata are halite and polyhalite; no common gypsum is found; 2) analyses of homogenization temperatures of halite fluid inclusions indicate that a higher temperature is needed for polyhalite generation compared with other saline minerals; and 3) the fluid inclusion chemical analysis shows that they are sulfate-type minerals with a shortage of Ca. Thus, it can be concluded that the formation of polyhalite is not related to gypsum replacement, and deep oilfield brines may provide a Ca source and a higher temperature for polyhalite formation, where the mixing and interaction occurred between K- and Mg-enriched sulfate brines and deep Ca-enriched brines under the control of climate and tectonics in the study area. While most polyhalite was generated natively, some formed during secondary generation, which was potentially related to replacement with carnallites or sylvites.

Chronological and rock magnetic constraints on the transition of the Quaternary paleoclimate in the western Qaidam Basin, NE Tibetan Plateau

A closed Quaternary saline paleolake, currently still a lake and named Dalangtan after one of its largest sub-basins, has widely distributed sediments in the western Qaidam Basin, NE Tibetan Plateau. Lacustrine salt minerals and fine sediments from this paleolake provide an environmental record for investigating paleoclimatic evolution in the Asian interior. However, detailed continuous Pliocene–Quaternary paleoclimatic records are broadly lacking from the NE Tibetan Plateau owing to poor exposure of the outcrops in section. For this study, we performed a detailed magnetostratigraphic dating and rock magnetic analysis on a 590-m-long core from the SG-5 borehole in the western Qaidam Basin. The results demonstrate that the lacustrine sediments in the SG-5 borehole were deposited more than ~3.0 Ma. Saline minerals began to increase at 1.2 Ma, and the magnetic susceptibility (χ) also changed at that time; the percentage frequency-dependent magnetic susceptibility was relatively low and uniform throughout the whole core. These observations, combined with the χ, pollen, salt ion, and grain-size records from other boreholes, indicate that the western Qaidam Basin and the greater Asian interior had a significant climate transition at 1.2 Ma during an extreme drought.

A Rapid Cu Enrichment Mechanism from Cu-Bearing Brine in Kuqa Basin, Xinjiang, China: Controlled by Crystallized Sequence of Saline Minerals

Sediment-hosted copper deposit is usually related to arid climate, ancient saline lake basin, and brine. The Kuqa Basin filled with giant-thickness evaporite units is located in the northern Tarim Basin, Xinjiang, China. It is famous for sandstone-hosted Cu deposits formed by synsedimentary processes. However, our recent studies reveal that Cu enrichment is closely related to brine on the surface of clastic rocks in the basin. It is shown that green Cu mineral coexisting with halite and gypsum occurred in the fractured fault belts of sandstones or was precipitated with halite on the surface of maroon clay in the scallops of sandstone. By SEM, EDS, and geochemical analysis methods on Cu-mineralized solid samples and brines, respectively, combined with previous geological evidence, our studies demonstrate that green Cu mineral is paratacamite, and it occurred with gypsum, halite, secondary glauberite, natural copper, and probably lead chloride on the fractured fault belts of sandstones or surface of clay. Meanwhile, the precipitation of paratacamite is controlled by a crystallized sequence of saline minerals accompanying with evaporated-concentrated course of brine in which gypsum, secondary glauberite, paratacamite, and halite are crystallized in turn. The Cu-bearing brine derived from meteoric waters and ancient seawater has a powerful capacity to leach metallic ions from its surrounding rocks and can be formed in a very short time (10 days is OK) in normal pressure and temperature conditions; also, the cycle of surface-Cu enrichment (mineralization) is only a few months (no more than 5). These indicate that a rapid Cu enrichment mechanism from Cu-bearing brine occurs on the earth’s surface of the evaporite basin. The mechanism might be supposed to make an enormous amount of metal mineralization in a short time if considered from a large-scale spatial viewpoint. By contrast with the lengthy geological period, the short evolutionary cycle of Cu enrichment (mineralization) is obviously different from the previous cognition.

New Combined Depressant/Collectors System for the Separation of Powellite from Dolomite and the Interaction Mechanism

The flotation beneficiation of powellite from dolomite was achieved with a new reagent system that consists of a mixed collector of sodium oleate (NaOl) and benzohydroxamic acid (BHA) and a depressant sodium hexametaphosphate (SHMP). The interaction mechanism of the reagent regime with minerals was studied using zeta potential and X-ray photoelectron spectroscopy (XPS) detection together with crystal chemistry and interaction energy analysis. The matching features of O–O distance in BHA with that in saline minerals and active site density/activity were used as methods to explain the reagent/mineral interaction. The results of microflotation finally established the new reagent regime at pH 8–12: 2.5 × 10−4 M SHMP, 2 × 10−4 M mixed collector containing 1.5 × 10−4 M NaOl and 0.5 × 10−4 M BHA. SHMP selectively depresses the adsorption of NaOl and BHA onto dolomite but minimally affects the adsorption of NaOl and BHA on the powellite surface.

Experimental Study on Foci Development in Mortar Using Seawater and Sand

Mortar using seawater and sand was the material studied here. The mortar specimens, in particular, were cured in natural seawater. The foci development in the mortar was the principal interest in this study. The on-line damage detection experiment art, including dynamically global MSHCT (Multi-Slices Helical Computer Tomography) scan and the local detection of EDS (Energy Dispersive Spectrometer), SEM (Scanning Electron Microscopy), and XRD (X-ray Diffraction) was designed to research the foci development in the mortar specimen. The mortar specimens with 70-day age were produced and investigated by the on-line damage detection experiments. The experiment results indicated that the mortar using seawater and sand offered appreciable strength at the early age, at least, although some saline minerals were generated during the preparation. The residual strength of the mortar was above 13 MPa, which helped to prevent the sharp damage of engineering bodies. The micro-interfacial behavior and the parental foci development controlled the damage evolution in the mortar using seawater and sand, the performance of which was still the adjustable one by composition optimization.