Degree of Brine Evaporation and Origin of the Mengyejing Potash Deposit: Evidence from Fluid Inclusions in Halite

The Mengyejing potash deposit is located in the southern port of the Simao Basin, Yunnan Province, and is hosted in mid-Cretaceous strata. The chemical compositions of fluid inclusions in halite crystals, collected from the level-610 adit in the deposit, were analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results show that the brine is of the Na-K-Mg-Ca-Cl type and has K concentrations that are distinctly higher than those of Mg and Ca, unlike normal brines associated with Cretaceous halite. The high K concentrations indicate that the degree of evaporation of the ancient Mengyejing saline lake was very high, reaching the sylvite deposition stage but rarely reaching the carnallite deposition stage. The trajectory of the H and O isotopic compositions of the brines in the halite-hosted fluid inclusions corresponds to intense evaporation, indicating that the net evaporation exceeded the net inflow of brines. These brine compositions in halite-hosted fluid inclusions were likely formed by the dissolution of previously deposited K-bearing minerals by fresh continental and/or seawater, forming a type of modified seawater, with deep hydrothermal fluids potentially supplying additional potassium. The basin likely experienced multiple seawater incursion, dissolution and redeposition events in a high-temperature environment with high evaporation rates.     

Ore petrology,hydrothermal alteration,fluid inclusions,and sulfur stable isotopes of the Milin Kamak intermediate sulfidation epithermal Au-Ag deposit in Western Srednogorie,Bulgaria

The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50 km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Milin Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000 m, widths from several cm to 3–4 m, rarely to 10–15 m, an average of 80–90 m depth (a maximum of 200 m) and dip steeply to the south. The average content of gold is 5.04 g/t and silver – 13.01 g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H₂O-rich with homogenization temperature (T_h) ranging from 238 to 345 °C as the majority of the measurements are in the range 238–273 °C. Ice-melting temperatures (T_m) range from −2.2 to −4.1 °C, salinity – from 3.7 to 6.6 wt.% NaCl equiv. These measurements imply an epithermal environment and low- to moderate salinity of the ore-forming fluids.δ³⁴S values of pyrite range from −0.49 to +2.44‰. The average calculated δ³⁴S values are 1.35‰. The total range of δ³⁴S values for pyrite are close to zero suggesting a magmatic source for the sulfur.     

Early Cretaceous tungsten mineralization in Southeastern China: the Wuning example

The Wuning tungsten deposits in northwestern Jiangxi are located in the Middle-Lower Yangtze River metallogenic belt of SE China. This article decodes the large tungsten-mineralized ore field by analysing three typical deposits: Shimensi, Dahutang, and Shiwendong. The Shimensi deposit shows three mineralization styles, and the associated hydrothermal alteration mainly includes K-feldspathization, greisenization, chloritization, silicification, and carbonatization. The sulphur isotopic compositions of sulphides in the Dahutang deposit indicate that the sulphur source was homogeneous and closely related to magmatic sulphur. The lead isotopic compositions of sulphides suggest multiple sources that were also closely related to magmatism. The carbon isotopic compositions of calcite indicate that hydrothermal fluids were derived from the granitic magma. Hydrogen and oxygen isotopic compositions of quartz veins indicate that the ore-forming fluids had a magmatic-hydrothermal origin, but mixed with meteoric water. Fluid inclusions from the Shiweidong deposit are low density, indicating medium-high T and low-medium salinity, further suggesting that it was a shallow magmatic-hydrothermal deposit, and the metallogenic hydrotherm mingled with the surface water late in the evolution of the system. Mineralization was related to Early Cretaceous magmatism in eastern China. The subduction of the palaeo-Pacific plate and the subsequent lithospheric delamination reflected transition from a compressional to extensional tectonic regime. The upwelling of the hot asthenosphere triggered partial melting of the Neoproterozoic Shuangqiaoshan Group, with high W background concentrations. The ascent of the magma resulted in the exsolution of the ore-bearing magmatic hydrothermal fluid.     

成渝城市群对县域城镇影响区分析

采用地理国情监测数据和统计数据,研究识别城镇的社会经济影响区范围,对成渝城市群在四川的113个县域,从城镇综合实力、可达性、影响力及城镇影响区特征进行分析。研究结果表明,形成了以覆盖成都、德阳、绵阳、眉山与资阳为核心的强影响力空间连片区,与其他县域城镇综合实力的极化现象较为突出。主要存在影响区扩展的城镇,扩展的影响区域已明显覆盖了相邻县城的影响区,较好地呈现出这部分县域经济正趋于融合,形成多极点的县域经济协同发展模式。     

板溪锑矿床流体包裹体研究

板溪锑矿床是湘中锑矿矿集区内的一个中型石英脉型锑矿床,赋存于板溪群五强溪组浅变质碎屑岩中,受NE向的桃江—城步断裂带控制。流体包裹体研究表明,板溪锑矿流体包裹体类型包括富液相水溶液包裹体(Ⅰ型)、富二氧化碳包裹体(Ⅱ型)、纯液相包裹体(Ⅲ型)三类;流体盐度为w(NaCl,eq)=3.4%~7.7%,均一温度为181~331℃,流体的密度为0.78~0.92g/cm~3,矿区成矿流体具有中低温、低盐度、低密度的特点,成矿流体的pH值为5.72,估计成矿压力为49~91 MPa,成矿的地壳深度为5.6~7.8km;均一温度与盐度呈正相关关系,成矿过程中两种流体发生混合作用而成矿。     

黑龙江宁安英城子金矿床的地质、流体包裹体特征与成因研究

英城子金矿床是典型的浅成热液型矿床,为确定矿床成矿条件,结合矿床地质特征同时对不同深度的同一条含金石英脉中的流体包裹体分别进行了显微测温和激光拉曼光谱的分析研究。研究结果表明:英城子金矿床矿石类型主要为蚀变岩型,其次为石英脉型;成矿过程分为以下4个阶段:(Ⅰ)石英-毒砂-黄铁矿阶段、(Ⅱ)石英-黄铁矿阶段、(Ⅲ)石英-多金属硫化物阶段、(Ⅳ)石英-硫化物阶段;流体包裹体的类型多数为气液两相,少数为气、液单相或三相包体,均一温度变化范围247.9℃~400.0℃,盐度[w(NaCl)]为3.15%~7.70%,成矿流体密度为0.65 g/cm3~0.87g/cm~3;结合包裹体激光拉曼光谱数据确定成矿流体属于中低温,中低盐度的CO_2-H_2O-NaCl体系;根据测温数据,该矿床的成矿压力为6~50 MPa、相应就位深度为0.11~0.65 km;由此可推测该矿床是与韧性变形作用有关的中温中压热液金矿床。结合前人有关成矿年代学的研究成果,可以进一步确认成矿作用发生在晚二叠世末亚洲洋壳俯冲作用晚期,且与陆内松嫩板块和佳木斯板块碰撞过程中构造体制的转换紧密相关。     

川中南部地区下二叠统栖霞组白云岩储层成因研究

川中南部地区下二叠统栖霞组在钻探中发现栖二段细—中晶白云岩是良好的储层,并且多口井获得工业气流,展示出一定勘探潜力。为进一步预测川中南部地区白云岩的储层分布特征,加快研究区下一步勘探开发,应用储层岩性特征识别、碳氧同位素、包裹体测温、阴极发光以及稀土元素分析研究白云岩储层成因,结果表明栖霞组白云岩无石膏或其他蒸发盐岩伴生,储集岩以细—中晶白云岩和灰质白云岩为主,主要分布于栖二段;栖霞组白云岩C、O同位素测试δ13C为4.03‰~4.77‰、古盐度为131.74~133.39,包裹体均一温度为110~180℃,阴极发光较弱,基质白云岩发紫红色光,溶洞充填马鞍状白云岩不发光;稀土元素的轻稀土和重稀土分布趋势一致,保持了原岩的稀土配分趋势;综合分析认为栖二段白云岩为埋藏成因,其中裂缝和溶洞充填的马鞍状白云岩为热液成因。      

基于Sentinel-1A雷达影像的崇明东滩芦苇盐沼植被识别提取

为研究芦苇盐沼植物在一个生长周期不同生长季节的雷达后向散射系数变化特征,对芦苇分布信息进行提取,探究Sentinel-1A卫星数据在长江口湿地植被监测中的应用前景。以对长江河口崇明东滩南部为研究区域,利用2016年11个时相的Sentinel-1A雷达卫星影像VV（vertical transmit/vertical receive）+VH（vertical transmit/horizontal receive）双极化数据,分析潮滩地带芦苇、白茅、海三棱藨草、水体和光滩在植被生长周期内的雷达后向散射强度变化特征,对芦苇盐沼植被进行识别提取。结果表明：相较于VH极化方式,VV极化方式下不同地物的后向散射强度差异更为明显,芦苇的后向散射强度在枯叶期下显著高于其他地物;进行芦苇植被提取时,需要对植被枯萎期不同潮位状况下的雷达影像进行组合运算,芦苇提取精度可达到88.7%;对芦苇植被雷达后向散射强度和临近时相的光学遥感归一化植被指数（normalized difference vegetation index,I_NDV）进行相关性分析,发现两者呈良好的正相关关系,相关系数为0.78。     

He-Ar Isotopic Systematics of Fluid Inclusions in Pyrites from PGEpolymetallic Deposits in Lower Cambrian Black Rock Series, South China

He-Ar isotopic compositions of fluid inclusions trapped in pyrites from some representative PGE-polymetallic deposits in Lower Cambrian black rock series in South China were analyzed by using an inert gas isotopic mass spectrometer. The results show that the ore-forming fluids possess a low 3He/4He ratio, varying from 0.43×10-8 to 26.39×10-8, with corresponding R/Ra value of 0.003-0.189. The 40Ar/36Ar ratios are 258-287, close to those of air saturated water (ASW). He-Ar isotopic indicator studies show that the ore-forming fluids were mainly derived from the formation water or basinal hot brine and sea water, while the content of mantle-derived fluid or deep-derived magmatic water might be negligible. The PGE-polymetallic mineralization might be related to the evolution of the Caledonian miogeosynclines distributed along the southern margin of the Yangtze Craton. During the Early Cambrian, the formation water or basinal hot brine trapped in Caledonian basins which accumulated giant thick sediments was