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Little attention has been paid to the study of sedimentary records from DaQaidam Salt Lake regarding brine evolution and hydro-climate change. Here we report the results of AMS 14C dating and mineralogical investigation on a sediment profile D4 from the south central of perennial saline water-body. The result revealed that pinnoite deposit in the lakebed was formed in early Holocene, the lake underwent three stages of lake-level and brine evolution in Holocene period, which were determined mainly by precipitation-controlled catchment inflow. The mineralogical records also depicted fluctuations in lake level and hydrochemistry on decadal and centennial scales.

Da Qaidam Salt Lake, northern Qaidam Basin, is known for its liquid and solid boron resource. More than that, pinnoite-bearing sediments, occurring in this lake, are rare in the world. However, little attention has been paid to the hydro-climate change and brine evolution correlation with the formation of pinnoite deposit. According to the multi-proxy records, as well as AMS 14C dating, the sediment profiles DCD02 and DCD03 from Da Qaidam Salt Lake were studied. The results revealed that the ore-forming age of three pinnoite deposits are 7.83–8.62 cal ka BP, 6.74–7.07 cal ka BP and 4.66–5.41 cal ka BP. The sedimentary evolution of Da Qaidam Salt Lake along with the pinnoite formation during the past 13,000 years can be divided into four stages, i.e., (1) relatively fresh and deep paleo-lake with low salinity during 12.98–9.00 cal ka BP; (2) seasonal variations between fresh and brackish paleo-lake during 9.00–8.62 cal ka BP; (3) salt lake stage with relatively high salinity and alkalinity during 8.62–4.66 cal ka BP, and (4) relatively shallow lake with high salinity since 4.66 cal ka BP. Under favorable sedimentologic and hydrogeochemical conditions, a series of boron deposits including pinnoite ore formed in different zones of Da Qaidam Salt Lake due to the different ore-forming mechanisms. Finally, under the differential effect of climate warming condition between the high mountain catchments and arid basin, the boron ore-forming model was established as a higher mountain–lower basin–shallower water model.

Mineralogy is very important in the study of lake, especially in the study of regional and past global change using lake sediments. In the final analysis, mineralogy could be involved in the study of the in-depth mechanism of lake sediments. In this paper, analysis the minerals by XRD in the sediments of Toson lake in the northeast of Qinghai-Tibet Plateau, the results showed that the main minerals in Toson lake were aragonite, calcite, quartz, halite, albite, muscovite, clinochlore and dolomite. And the main categories were detrital minerals and carbonate minerals with obvious reverse correlation. It suggested that Toson lake was mainly situated carbonate sedimentary stage, and the input of carbonate was lacustrine authigenic carbonate.

An integrated analysis has been carried out on core dated by qualitative X-ray fluorescence core scanning combination of quantitative ICP-AES in order to characterize the extent of elements Cd, Cr, Cu, Zn, and Pb in the Lake Toson in the northeastern Tibet Plateau. When combining both the quantitative and qualitative measurements, we observed a significantly positive correlation. Comparing the ratios between element intensities and concentration, we found that the XRF element intensities were related to the amount of water. Using the intensity of Cl as an indicator of water content, the element intensities of Cd, Cr, Cu, Zn, and Pb in the core samples were corrected. The correlation coefficients of each pairs of the two datasets among Cd, Cr, Cu, Zn, and Pb were significantly raised. These data sets with highly correlations were used to produce a transfer function to relate XRF element intensity with element concentration. Calculated element concentrations from the intensities show only minor differences from concentrations obtained by ICP-AES, indicating XRF core scanners are a very useful tool for measuring element concentration in lacustrine sediments.

The pinnoite deposit occurred in the lakebed of Da Qaidam Salt Lake in Qaidam Basin is rare in the world. This study focused on the pinnoite, ulexite and hydroboracite from Da Qaidam Salt Lake, through multi-index methods including mineralogy and geochemistry, aiming to interpret the mechanism of pinnoite and other borate minerals. The results showed that pinnoite as well as ulexite and hydroboracite in lakeside are formed in the lake environment with specific hydrogeochemical conditions (e.g., alkaline brine, hydrochemical types, boron concentration, boron ions, Mg/Ca ratio, dilution and mixing mechanism). The borate formation was controlled by a coupling mechanism, i.e., the inherent geochemical characteristics and the external conditions.

The paper focused on the study of detrital yellow layer from sediment profile D3 of DaQaidam Salt Lake, based on AMS 14C chronologic and mineralogical methods, aimed to discuss the dust storm events recorded by detrital yellow layer of DaQaidam region since Late Glacial period. The results showed that the grain-size distribution curve displayed double kurtosis, the main peak (10 µm in average) reflected the fine-grained fractions into lake by fluviation, and the secondary peak (> 32 µm) reflected the coarse silt fractions into lake by wind effect and fluviation. Finally, the coarse-grained fractions (> 64 µm) from sediment profile D3 probably recorded the dust storm events since Late Glacial period.

Environmental changes influenced by human activities were recorded in the sediment cores from Xingyun lake. Based on the 137Cs and 210Pb dating, multi-proxy records, enrichment factor (EF), and geoaccumulation index (Igeo) methods, the history of human–environment interactions in Xingyun lake catchment during the past 140 years was studied. The results showed that the total heavy metal pollution in Xingyun lake followed the decreasing order: the northwestern > the middle > the southwestern > the southern > the north easterly. These distributions were controlled by regional geochemical background values, pollution load, and the lake current driven by prevailing southwesterly winds. The total EF value of heavy metals followed the decreasing order: EF (Zn) > EF (Cr) > EF (Pb) > EF (Cd) > EF (Cu). The total Igeo value of heavy metals also followed the decreasing order: Igeo (Zn) > Igeo (Cr) > Igeo (Pb) > Igeo (Cd) > Igeo (Cu). Consequently, the total pollution level of heavy metals followed the decreasing order: Zn > Cr > Pb > Cd > Cu. Before 1910 AD, the natural erosion caused by climate changes was the key factor for the heavy metals accumulated. After 1910 AD, the heavy metal concentrations were mainly controlled by anthropogenic impacts, the dominant sources were from industrial pollution, agricultural pollution, mining, and organic degradation. Finally, the sedimentary evolution history of Xingyun lake can be divided into four stages, i.e., (1) natural evolution stage during 1862–1910 AD, (2) anthropogenic disturbance stage during 1910–1953 AD, (3) anthropogenic reconstruction stage during 1953–1984 AD, and (4) eutrophication stage after 1984 AD.

Mg-borates were traditionally thought to be diagenetic products of other primary borate minerals. Here we report results from the study of pinnoite deposit from DaQaidam saline lake, indicating that pinnoite minerals are primary in origin. Within the detecting limit of X-ray powder diffraction analysis (XRD) analysis, no other borate minerals than pinnoite are detected from the Mg-borate deposit. The cemented pinnoite orebody shows the sedimentary structure of light-dark lamination couplets, which signal marked seasonal variations in brine chemistry. The scanning electronic microscopy coupled with an energy dispersive X-ray spectrometer (SEM-EDX) examination reveals that all pinnoite minerals displayed euhedral, giving no indication of diagenetic origin. A marked shift in lithology from clastic sediment to evaporitic deposit reflects a critical change in sedimentation regime associated with abrupt changes in hydroclimatic conditions. The deposition of the pinnoite ore-layer containing abundant hydromagnesite marked the beginning of the evaporite formation and the end of the clastic deposition. This suggests that aridification occurred abruptly and the saline lake was much more alkaline than today in the early-stage of the evaporite deposition. The intensified summer evaporation and seasonal variations in water chemistry brought about a shallow to nearly desiccated paleo-lake with pH exceeding 9.3, Mg/Ca ratio &gt, 39, and boron concentration &gt, 600 mg/L, which favored pinnoite precipitation and the formation of pinnoite deposit in the central DaQaidam saline lake.

Qaidam Basin is a hyperarid inland basin with an area of 121 × 10 3 km 2 located on the northern Tibetan Plateau. Today, one fourth of the basin is covered by playas and hypersaline lakes. Nearly 80% of brine lithium found in China is contained in four salt lakes: Bieletan (BLT), DongTaijinaier (DT), XiTaijinaier (XT) and Yiliping (YLP). In the past decade, great attention was paid to improving the technology for the extraction of lithium from the brine deposits, but studies on origin and mode of formation of the brine deposits remained limited. Our recent investigations found that: (1) ~ 748.8 t of lithium was transported annually into the lower catchment of the four salt lakes via the Hongshui–Nalinggele River (H–N River), the largest river draining into the Qaidam Basin, (2) Li + -rich brines are formed only in salt lakes associated with inflowing rivers with Li + concentrations greater than 0.4 mg/L, and (3) the water Li + concentration is positively correlated with both the inflowing river and the associated subsurface brine, including saline lakes with low lithium concentrations. These findings clearly indicate that long-term input of Li + from the H–N River controls the formation of lithium brine deposits. Here we determine that the source of the lithium is from hydrothermal fields where two active faults converge in the upper reach of the Hongshui River. The hydrothermal fields are associated with a magmatic heat source, as suggested by the high Li + and As 3 + content water from geysers. Based on the assumption of a constant rate of lithium influx, we estimate that the total reserves of lithium were likely formed since the postglacial period. Our data indicate that lithium reserves in each of the four salt lakes depend on the influx of Li + -bearing water from the H–N River. The data also suggest that during the progradation of the alluvial Fan I, the H–N River drained mostly into the BLT salt lake until the Taijinaier River shifted watercourse to the north and began to feed the salt lakes of the DT, XT and YLP, alongside with the Fan II progradation. The inference is consistent with stratigraphic evidence from the sediment cores of the four salt lakes. One of the major findings of our work is the importance of the contrasting hydroclimatic conditions between the high mountains containing ice caps and the terminal salt lakes. The greater than 4000 m of relief in the watershed enables a massive amount of ions, such as K + , to be weathered and transported together with detrital material from the huge, relatively wet alpine regions to the hyperarid terminal basins, where intense evaporation rapidly enriches the lake water, resulting in evaporite deposition and associated K + - and Li + -rich brine deposits.

The deep, tight gas reservoir in the Daqing oil field, P. R. China has multiple parallel sandy conglomerates with horizontal heterogeneity and poor historical production from vertical wells and single-lateral horizontal wells. These blocks comprise a large volcanic gas reservoir, which is also challenging for directional drilling. This paper describes a dual-lateral completion with hydraulic fracturing that addresses these production issues. To deploy a stacked dual-lateral well in this reservoir, the deep well depth and its high temperature are considered. The junction must be sealed because of the borehole stability and gas. Re-entry to both laterals, temporarily isolation of laterals, openhole multi-stage hydraulic fracturing and commingled production was possible with a multilateral completion system. This was the operator's first installation of this technology. As a result of comprehensive study, the TAML Level 4 Hook Hanger Multilateral System and One-trip Open Hole Multi-stage Frac System were selected. The junction was successfully cemented after installation of the Hook Hanger System. Each lateral was installed with more than 10 stages of frac system completion tools. After both laterals were hydraulically frac and flow tested, the commingled upper completion string was installed for commercial production. The application of multilateral technology in this field was completed safely. Gas production rates from the multilateral well tested 4.3 times greater than the average production rate from the three offset vertical wells. The absolute open flow rate achieved was more than 1MMSCM, which is the biggest producer for tight gas reservoir in Daqing area. This production rate indicated that the dual-lateral well fracture completion method was applicable for this reservoir.