Effect of coal mine waters of variable pH on springwater quality: A case study

Disruption of coal strata during mining accelerates pyrite oxidation by exposing greater surface areas of the reactive mineral to weathering. Acidic water in a coal mine in the Niangziguan spring watershed is related to this process and is characterized by low pH (min. 2.52) and high sulfate (max. 4100 mg/I), iron (max. 257 mg/I), and hardness (max. 2274.45 mg/I). However, it is possible that the kind of acidic coal mine water is subsequently neutralized because of the dissolution of calcite present in the coal strata. The hydrochemical characters of the alkaline coal mine water produced are high pH (max. 8.18), sulfate (max. 542 mg/I), and hardness (max. 1183.56 mg/I) and lower iron (min. 0.12 mg/I). Experiments were conducted to further understand the mechanism of the formation of both acidic and alkaline waters in the spring watershed coal mines by modeling natural conditions with simplification, and the results of the experiments have shown that they are basically successful. The high sulfate (max. 223.82 mg/I) and hardness (max. 435.53 mg/I) of the Niangziguan springs are related to the influence of the neutralized acid coal mine water as demonstrated by analysis of water temperature, total dissolved solid, Q-mode cluster analysis, and sulfur isotopes. The influence of the neutralized acid coal mine water on the pH and iron in the springs is not obvious because of the neutralization effect of calcite in aquifer, the buffer effect of groundwater, and the precipitation of iron. Some measures to prevent the formation of acid and alkaline coal mine water are presented.     

Water contamination and remedial measures at the Troya abandoned Pb-Zn mine (The Basque Country, Northern Spain)

 This article describes a case of contamination of a karstic aquifer by abandoning an underground mine exploiting sulphide ore body. To exploit the ore, the aquifer was drained and the water level declined about 230 m, drying up the spring that had drained the aquifer up to that moment. When the mining activity ceased, the piezometric level recovered and contaminated water began to flow out from a mine adit. The water is high in sulphates and dissolved Fe, although the pH is neutral. When this water reached the nearby creek, the fish population was eliminated, principally due to the presence of toxic metals and the precipitation of Fe hydroxides. The contamination originated in an area of the partially flooded mine rooms where the ore is in contact with both air and water. The acidity generated by pyrite oxidation is neutralized by calcite dissolution. Presently, the mine water is diverted to the old tailings pond which functions as an aerobic wetland. This action has allowed the fish population in the creek to be restored. Received: 20 January 1999 · Accepted: 15 March 1999     

Investigation of pyrite oxidation and acid mine drainage characterization associated with Razi active coal mine and coal washing waste dumps in the Azad shahr–Ramian region,northeast Iran

Acid mine drainage (AMD) pollution is considered to be the most serious water pollution problem in mining areas. AMD containing iron sulfates and other components can affect the receiving water bodies. Pyrite oxidation and AMD generation can be considered as important processes that may take place in the wastes produced by coal mining and coal washing operations in the Golestan province (northeast Iran). The study area is characterized by appropriate atmospheric conditions that favor pyrite oxidation and the presence of a large amount of water bodies. This study attempts to consider pyrite oxidation and AMD generation in the Azad shahr–Ramian region. The impact of AMD on the quality of the surface water bodies was investigated by taking samples and analyzing them for hydro-geochemical parameters. Stiff and Piper diagrams were used to represent chemical analyses of water samples. The coal samples taken from different depths at four points on two different coal waste dumps were analyzed to find the fraction of pyrite that remained in the waste particles to investigate the pyrite oxidation process. A computational fluid dynamic package called PHOENICS was used to model pyrite oxidation process numerically. The results obtained from the geochemical analyses of water and coal samples and numerical simulation show pyrite oxidation and acid generation in the region. However, the presence of carbonate rocks raised the pH of the water samples. The drainages of the Razi mine may be recognized as natural alkaline mine drainages.     

煤矿酸性“老窑水”低Ca/Mg成因机制

山西省阳泉市山底河煤矿“老窑水”循环系统多年水质监测数据计算结果显示,煤矿酸性“老窑水”的Ca/Mg值普遍偏低,且存在Ca/Mg值随酸化程度的增强（SO₄2?含量增加或pH减小）而减小的规律。针对这一问题,结合研究区的地球化学物源条件,通过室内试验以及野外监测水样的石膏、方解石、白云石矿物饱和指数与pH变化关系,分析煤矿酸性“老窑水”低Ca/Mg值的成因机制。研究表明:区内石炭系－二叠系的煤系地层中碳酸盐岩夹层、分散状态分布的菱镁矿、黄铁矿是“老窑水”中Ca2+、Mg2+、SO₄2?的物质来源;在黄铁矿氧化水解形成的以硫酸根为主导的酸性溶液中（pH为2.0~4.5）,代表硫酸对石膏、方解石、白云石可溶解性的饱和指数排序为石膏>方解石>白云石,受石膏在高浓度硫酸活性降低并发生沉淀、方解石溶解受Ca2+同离子效应抑制和饱和状态的平衡调节的综合影响,使Ca2+相对含量减少,由于MgSO₄溶度积大于CaSO₄,故Mg2+含量未受上述约束（或较低）,脱白云岩化反应可因Ca2+含量随石膏沉淀而继续进行,加之区内有菱镁矿的溶解,使得Mg2+相对含量增加,最终出现了镁矿酸性“老窑水” Ca/Mg值低的结果。Ca/Mg值可作为煤矿酸性“老窑水”的污染特征指标,应用于环境影响评价。      

A mineral quantification method for wall rocks at open pit mines,and application to the Martha Au–Ag mine,Waihi, New Zealand

Pit lakes that result from open pit mining are potential water resources or potential environmental problems, depending on lake water quality. Wall rock mineralogy can affect lake chemistry if surface water inputs and/or groundwater inputs and/or lake water in contact with submerged wall rocks react with the wall rock minerals. This study presents a mineral quantification method to measure the distribution and concentration of wall rock minerals in open pit mines, and applies the method to the Martha epithermal Au–Ag mine, Waihi, New Zealand. Heterogeneous ore deposits, like Martha, require a large number of wall rock samples to accurately define mineral distributions. X-ray diffraction analyses of 125 wall rock samples identified the most abundant minerals in the wall rocks as quartz, adularia, albite, illite, chlorite, kaolinite, pyrite and calcite. Distribution maps of these minerals defined 8 relatively homogenous areas of wall rock referred to as “mineral associations”: weakly-altered, propylitic, fresh-argillic, weathered-argillic, oxidized, potassic, quartz veins, and post-mineralization deposits. X-ray fluorescence, Leco furnace, and neutron activation analyses of 46 representative samples produced the geochemical dataset used to assign quantities of elements to observed minerals, and to calculate average mineral concentrations in each association. Thin-section petrography and calcite concentrations from Sobek acid-digestions confirm the calculated mineralogy, providing validation for the method. Calcite and pyrite concentrations allowed advanced acid–base accounting for each mineral association, identifying 3 potential acid-producing associations and one potential acid-neutralizing association. The results target areas, where detailed hydrologic and kinetic tests would be valuable in the next stage of pit lake evaluation. Detailed understanding of wall rock mineralogy will help strengthen predictions of pit lake water quality.     

Characterization of Kolar gold field mine tailings for cyanide and acid drainage

The gold mining process at Kolar gold field (KGF) mines has generated about 32 million tons of tailings. Gold was extracted from the mined ores using cyanidation technique that involved dissolution of gold in the ore by water soluble alkali metal cyanides (example, sodium cyanide or potassium cyanide). Of the several dumps that received the mine tailings only the Kennedy’s Line dump was active prior to closure of the KGF mines in the year 2000. The Kennedy’s Line dump received sulfide bearing tailings in slurry form that comprised of spent ore and process water bearing soluble alkali metal cyanide. Depending on the pH of the tailing slurry, the free cyanides may exist as aqueous hydrogen cyanide that can escape to the atmosphere as hydrogen cyanide gas or occur as soluble cyanide (CN⁻) ions that can be leached by infiltrating water to the sub-surface environment. Additionally, the presence of pyrite minerals in the Kennedy’s Line dump makes them susceptible to acid drainage. This study examines the potential of gold tailings of Kennedy’s Line dump to release cyanide ions (CN⁻) and acid drainage to the sub-surface environment by performing physico-chemical and leaching tests with tailing samples collected from various depths of the dump, sub-surface soil samples beneath the dump and groundwater samples from vicinity of Kennedy’s Line dump. The chemical mechanisms responsible for the ambient cyanide and pH levels of the tailing dump, sub-surface soil samples and groundwater are also inferred from the laboratory results.     

An experimental study of water–rock interaction and acid rock drainage in the Butte mining district,Montana

. This paper summarizes a laboratory study of water–rock interaction and the generation of acidic mine drainage in the Butte mining district, Montana. The Butte district includes two large open pit mines exploiting different portions of the same porphyry Cu–Mo system: (1) the well-known Berkeley Pit, which is abandoned and flooding with acidic mine water; and (2) the nearby Continental Pit, which is active. The two pits are separated by a normal fault with several thousand feet of vertical displacement, and consequently the styles of alteration and mineralization are quite different. Humidity cell and recirculating leachate experiments of crushed rock exposed on the walls of the Berkeley Pit produced effluent waters very similar in composition to the flooded Berkeley Pit lake. In contrast, the same experiments on crushed ore from the Continental Pit generated circum-neutral leachates with low metal concentrations, caused by the presence of calcite in the alteration assemblage. Because carbonate is being depleted at a faster rate than pyrite during weathering, the quality of mine drainage in the Continental Pit could eventually degrade.     

安徽泥河铁矿矿坑充水因素研究

安徽泥河铁矿矿区水文地质条件较复杂,矿体埋深大,在综合分析矿区水文地质条件、地表水、地下水相互水力联系的基础上,从岩层性质、地下水赋存及补给条件,确定了影响矿床充水的各因素,结果可知:泥河铁矿矿体埋藏深度大,顶底板围岩为隔水层,次生石英岩含水层为矿坑充水的主要间接补给源,其多位于矿体顶板之上50 m,受矿体上部导水性极弱的闪长玢岩层的限制,补给量微弱,对矿区大部分矿坑充水影响不大。但在矿区东北部和中部地段,受开采时冒落带以及导水裂隙带的影响,对该区域矿坑充水的影响较大。此次研究填补了该矿区深层地下水含水系统研究的空白,为准确预测矿坑涌水量提供理论依据,具有重要的参考价值和现实意义。     

河南嵩县下蒿坪金矿工艺矿物学研究

通过化学分析、扫描电镜以及工艺矿物学自动定量分析系统(MLA)等测试方法对河南嵩县下蒿坪金矿进行了系统的工艺矿物学研究,包括原矿化学组成、矿物组成、金的赋存状态、主要载金矿物嵌布特征以及矿物解离特性等。结果表明,该金矿中主要可回收的有价金属为金,其品位为3.75×10^-6。该金矿的原矿矿物主要由石英、钾长石、钠长石、黄铁矿和铁白云石组成,此外还有少量的赤铁矿、萤石、白云石以及方解石。原矿中的金主要赋存在黄铁矿中,而黄铁矿大部分以细粒、微细粒形式嵌布在石英和长石颗粒中。原矿中自然金的含量非常少,多以单独的自然金颗粒形式存在。原矿磨至P₈₀=0.074 mm(-0.074 mm粒级含量占80%)时载金矿物黄铁矿、方铅矿、闪锌矿的单体解离度相对较高,有利于通过浮选回收。     

Forms of Iron in the Phosphorites of Abu—Tartur Area,Egypt

The Campanian-Maastrichtian phosphatic deposits in Egypt,called the Duwi Forma-tion,comprise a part of the extensive Middle East to North African phosphogenic province of Late Cretaceous to Paleogene age.The province holds the greatest accumulation of phosphorites in the geological history,possibly in excess of 70 billion metric tons.The phosphate resources in Egypt alone exceed 3 billion metric tons.Two-third of these three billions occur only in the Abu-Tartur area.Among the phosphorite deposits in Egypt,the phosphorites of the Abu-Tartur area are characterized by high contents of iron ranging from 3% to 7% with an average of 5%.The detailed mineralogical and geochemical studies on the Abu-Tartur phosphorites revealed that iron is found in the form of pyrite,ankerite,clay minerals,microinclusions,and iron oxide.Pyrite,which is the major fraction,occurs as filling cement and partial to complete teplacement of phosphatic grains and confined to the fresh phosphorites while iron oxide occurs as cryp-tocrystalline aggregates of red to brown particles and is confined to the weathered outcrops.Ex-clusive relations between pyrite in the fresh phosphorite samples inside the Abu-Tartur mine and iron oxide in the equivalent horizon of the weathered exposure indicated that iron oxide was formed by the oxidation of pyrite as a result of weathering.All of these forms harm the quality of ore,manufacturing processes,and the produced phosphoric acid and fertilizers.     

重新集铁矿矿坑涌水量预测研究

针对重新集铁矿水文地质条件深入研究,对其进行相应概化,利用解析法以及数值法(分不同开采方案)进行矿坑涌水量预测,得出结论:解析法在矿坑涌水量中局限较大,在矿坑预测过程中更为推荐使用数值法,其预测结果与实际结果更为符合。从具体预测结果来看,最大矿坑涌水量均出现在首采阶段,而在全开采期矿坑涌水量总体变化不大。选择优先开采-160 m水平矿体和-300 m水平矿体两种不同的开采方案时,方案二的最大涌水量较小,有益于井下最大排水规模的控制,同时发现涌水量变幅也相对较平稳,有益于矿山水资源综合利用方案制定和矿山水环境治理方案的设计,建议矿床开采方案选择方案二。     

新疆乌恰炼铁厂地区铁矿床特征及成因分析

新疆乌恰炼铁厂地区石炭系碳酸盐岩建造中发育多处小型铁矿,这些铁矿床多受断层或构造裂隙控制,按照矿石矿物组构特征可划分为红山镜铁矿型铁矿和萨热塔什磁铁矿型铁矿,红山镜铁矿型铁矿石主要由镜铁矿、方解石和白云石等组成,萨热塔什铁矿石主要由磁铁矿、镜铁矿、黄铁矿和方解石、石英等组成。本文对两类铁矿床中的岩（矿）石进行了主量元素、微量元素和电子探针分析,研究认为,红山镜铁矿型铁矿和萨热塔什磁铁矿型铁矿的形成都与中石炭统康克林组碳酸盐岩沉积作用和后期构造叠加作用有关,前者成矿物质成分简单、成矿温度相对较低。后者成矿物质成分相对复杂、成矿温度也相对较高,除主要成矿物质来源于中石炭统康克林组碳酸盐岩沉积作用外,可能还有北东向深大断裂带中基性岩浆物质成分的混入。     

Geochemistry and petrography of REE-bearing Fe-oxide assemblages in Choghart iron deposit,Yazd, Iran

The Choghart magnetite-apatite deposit situated in the Bafq district, Central Iran, has been scrutinized for rare earth elements (REEs) by precise geochemical investigation. The Central Iran is a susceptible area of rare earth elements. One of the Choghart’s prominent points is the existence of hydrothermal zones which made prediction of REEs occurrence within the deposit possible. Choghart is placed within felsic volcanic tuffs, rhyolitic rocks, and volcanic sedimentary sections belonging to the lower Cambrian. Abundance and distribution pattern of REEs in Choghart iron deposits reveal a part of deposit formation and its mineralogical modifications. Petrography and mineralogy of the ore body demonstrated two main types of alterations (sodic and calcic) associated with iron ore mineralization in Choghart deposit. The main ore includes a large quantity of massive magnetite in the lower part of Choghart deposit. The minor mineralization involves apatite, pyrite, alkaline amphibole, especially actinolite and tremolite, calcite, talc, quart, monazite, and bastnasite. Geochemical sampling from north–northeast (N-NE) side of the mine denotes the presence of these elements in hydrothermal zones. Statistical populations of the area were categorized by fractal geometry into four main differentiations: host rock type (albitofyre), iron, metasomatose, phosphate zones, and a subset of the phosphate zone which is named high iron high phosphate type. REEs like lanthanum, neodymium, yttrium, and niobium constitute the most quantity of Choghart. Deposit characteristics demonstrate its similarity to Kiruna type. The significant feature of iron oxide-apatite deposits of Kiruna ore type is the existence of monazite inclusions within apatite. These inclusions were also observed within apatite type I and II of Choghart mineralization. Moreover, REEs geochemistry in Choghart deposit was identified by investigation on geochemical data analyses. The analysis represents negative Eu anomaly and further enrichment of light REEs compared to the heavy ones. Chondrite normalized REEs patterns are defined by negative anomalies of Eu, which is the main characteristic of Kiruna ore type. The results showed that REEs concentration in phosphate zone, as a high absorption of REEs, is much higher than metsomatose, albitofyre, and iron zones. REEs distribution in N-NE side of the mine indicated that the contact of iron ore with tailings in N-NW side of the mine leads REEs to be enriched nearly 1% , as well as that of NE with high contents of REEs 1.5% ), which is very significant.     

安徽庐枞盆地龙桥铁矿床中钴的赋存状态和空间分布规律

中国东部的长江中下游、莱芜、邯邢和临汾等矿集区中发育大量的矽卡岩型铁矿床,其中普遍伴生钴,部分矿床估算伴生钴资源量大于1万t,达到中型钴矿床的规模。已有研究表明,中国东部富钴矽卡岩型铁矿床的成矿时代相同,成矿特征相似,均为中国东部130Ma大规模成矿作用的产物,反映较大规模的铁钴成矿作用受统一的动力学背景控制。钴与其他伴生组分一样,其工业价值主要不取决于矿石中钴的含量,而取决于钴的赋存状态,因此开展矽卡岩型铁矿床中钴的赋存状态和分布规律研究具有重要的理论和实践意义。龙桥矽卡岩型铁矿床位于长江中下游成矿带,是目前发现的成矿带内伴生钴含量最高的矿床。矿床主矿体长1000m,成矿岩体位于矿体中部,黄铁矿分布范围广,距离岩体中心不同距离均有分布,是研究矽卡岩型铁矿床中钴赋存状态和空间分布规律的理想对象。本次研究在龙桥铁矿床勘探巷道-370m平面自西向东采集了9件含黄铁矿样品,黄铁矿主要呈浸染状-细脉状交代磁铁矿。研究表明,龙桥铁矿床中钴主要赋存在黄铁矿和磁铁矿中,其次为独立钴矿物(主要为辉砷钴矿)。黄铁矿的LA-ICP-MS微区微量元素分析结果表明,龙桥黄铁矿中Co(0.019×10~(-6)～5639×10~(-6))、Ni(0.025×10~(-6)～5798×10~(-6))和As(0.46×10~(-6)～14526×10~(-6))的含量均具有较大的变化范围,黄铁矿总体上具有边缘富钴、核部贫钴的特征,黄铁矿边部的钴含量是核部的100～1000倍。通过对LA-ICP-MS测试数据以及时间分辨率剖面的逐一对比,推测Co主要以类质同象形式替代Fe进入黄铁矿晶格。由于钴在黄铁矿中分布极不均匀,不同空间位置采集的黄铁矿样品中Co含量平均值和变化范围没有明显规律。本文通过类比,提出中国东部矽卡岩型铁矿床中钴矿物可能是普遍存在的,但以前受限于分析测试手段未能发现;如何在选矿过程中分离富集钴矿物和富钴黄铁矿,是矽卡岩型铁矿床硫精粉中钴回收利用的关键。     

Ordinary kriging and indicator kriging in the cartography of trace elements contamination in São Domingos mining site (Alentejo, Portugal)

The abandoned pyrite mine of São Domingos, in the southeast Portugal is still an acid mine drainage generator and a source for trace elements pollution. This study aims to evaluate and map the soils and sediments chemical pollution. With this purpose three test sites located in the vicinities of the mine were sampled for soils, sediments and mining waste materials. The samples were analysed for pH, organic carbon, iron oxides and total content of As, Cu, Cr, Hg, Pb, Sb, U, Zn, Mn, S, Fe Al, Ca, K, Mg and P. The hyperspectral image of the test sites was acquired using the aero transported sensor HymapTM. Chemical analysis and hyperspectral images data were processed to estimate the contamination maps by multivariate data analysis, ordinary kriging, cokriging and indicator kriging methodologies.The test sites located downstream the mine open pit, are highly contaminated mainly in As, Hg, Pb and Sb, but no contamination was found in the third test site, upstream the mining site. The acid mining drainage seems to be the main spreading agent of chemical contaminants mostly originating from the mine waste materials. Factorial analysis and the geostatistical methodologies allowed several approaches for the contamination cartography of mining areas.     

辽宁弓长岭铁矿床磁铁矿稀土元素特征及其地质意义

辽宁弓长岭铁矿床是我国著名的沉积变质型铁矿床,其二矿区的磁铁富矿达大型规模,属国内之最.为探讨弓长岭铁矿床铁矿的物质来源、形成环境和富矿成因,本文以二矿区六个铁矿体的贫铁矿石和富铁矿石中磁铁矿单矿物为研究对象,利用电感耦合等离子体质谱进行了系统的稀土元素测试.结果表明,所有样品中磁铁矿的稀土元素总量(∑REEs)和Y具有非常一致的特征:稀土元素总量较低,Y/Ho比值较高;经太古界后平均澳大利亚页岩( PAAS)标准化呈现重稀土相对富集、轻稀土相对亏损的分馏模式,大部分呈现La正异常,所有样品都有明显的Eu和Y正异常,这些特征表明研究区的磁铁矿成矿物质主要来源于海底高温热液和海水;虽然磁铁矿的Ce/Ce*为0.69～ 0.97,但大多数样品缺乏真正意义的Ce负异常,这暗示其沉积于还原的海水环境;富铁矿石磁铁矿的稀土元素总量和Eu含量明显高于贫铁矿石的磁铁矿,而且含富矿的上含铁带Eu异常明显较高,表明富铁矿石磁铁矿具有更明显的热液特征,是在贫铁矿石的基础上受热液活动形成的.     

Fluid Inclusion and Stable Isotope Study at the Southeastern Martabe Deposit: Purnama,Barani and Horas Ore Bodies,North Sumatra,Indonesia

The Martabe Au–Ag deposit, North Sumatra Province, Indonesia, is a high sulfidation epithermal deposit, which is hosted by Neogene sandstone, siltstone, volcanic breccia, and andesite to basaltic andesite of Angkola Formation. The deposit consists of six ore bodies that occurred as silicified massive ore (enargite–luzonite–pyrite–tetrahedrite–tellurides), quartz veins (tetrahedrite–galena–sphalerite–chalcopyrite), banded sulfide veins (pyrite–tetrahedrite–sphalerite–galena) and cavity filling. All ore bodies are controlled by N–S and NW–SE trending faults. The Barani and Horas ore bodies are located in the southeast of the Purnama ore body. Fluid inclusion microthermometry, and alunite‐pyrite and barite‐pyrite pairs sulfur isotopic geothermometry show slightly different formation temperatures among the ore bodies. Formation temperature and salinity of fluid inclusions of the Purnama ore body range from 200 to 260 C and from 6 to 8 wt.% NaCl equivalent, respectively. Formation temperature and salinity of fluid inclusions of the Barani ore body range from 200 to 220 °C and from 0 to 2.5 wt.% NaCl equivalent and those of the Horas ore body range from 240 to 275 °C and from 2 to 3 wt.% NaCl equivalent, respectively. The Barani and Horas ore bodies are less silicified and sulfides are less abundant than the Purnama ore body. A relationship between enthalpy and chloride content indicates mixing of hot saline fluids with cooler dilute fluids during the mineralization of each of the ore bodies. The δ¹⁸O values of quartz samples from the southeast ore bodies exhibit a wide range from +4.2 to +12.9‰ with an average value of +7.0‰. The δ¹⁸O values of H₂O estimated from δ¹⁸O values of quartz, barite and calcite confirm the oxygen isotopic shift to near meteoric water trend, which support the incorporation of meteoric water. Salinity of the fluid inclusions decrease from >5 wt.% NaCl equivalent in the Purnama ore body to <3 wt.% NaCl equivalent in the Barani ore body, indicating different fluid systems during mineralization. The δ³⁴S values of sulfide and sulfate in Purnama range from ? 4.2 to +5.5‰ and from +1.2 to +26.7‰, those in the Barani range from ? 4.3 to +26.4‰ and from +3.9 to +18.5‰ and those in the Horas ore body range from ? 11.8 to +3.5‰ and from +1.4 to +25.7‰, respectively. The δ³⁴S of total bulk sulfur in southeastern ore bodies (Σδ³⁴S) was estimated to be approximately +6‰. The estimated sulfur fugacity during formation of the Purnama and Horas ore bodies is relatively high. It was between 10^?4.8 and 10^?10.8 atm at 220 to 260 °C. Tellurium fugacity was between 10^?7.8 and 10^?9.5 atm at 260 °C and between 10^?9 and 10^?10.6 atm at 220 °C in the Purnama ore body. The Barani ore body was formed at lower fS₂, lower than about 10^?14 atm at 200 to 220 °C based on the presence of arsenopyrite and pyrrhotite in the early stage, and between 10^?14 and 10^?12 atm based on the existence of enargite and tennantite in the last stage. © 2016 The Society of Resource Geology     

Hydrogeochemical evaluation of groundwater in the lower Offin basin,Ghana

Alumino-silicate mineral dissolution, cation exchange, reductive dissolution of hematite and goethite, oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the Offin Basin. The main aim of this study was to characterise groundwater and delineate relevant water–rock interactions that control the evolution of water quality in Offin Basin, a major gold mining area in Ghana. Boreholes, dug wells, springs and mine drainage samples were analysed for major ions, minor and trace elements. Major ion study results show that the groundwater is, principally, Ca–Mg–HCO₃ or Na–Mg–Ca–HCO₃ in character, mildly acidic and low in conductivity. Groundwater acidification is principally due to natural biogeochemical processes. Though acidic, the groundwater has positive acid neutralising potential provided by the dissolution of alumino-silicates and mafic rocks. Trace elements’ loading (except arsenic and iron) of groundwater is generally low. Reductive dissolution of iron minerals in the presence of organic matter is responsible for high-iron concentration in areas underlain by granitoids. Elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation. Approximately 19 and 46% of the boreholes have arsenic and iron concentrations exceeding the WHO’s (Guidelines for drinking water quality. Final task group meeting. WHO Press, World Health Organization, Geneva, 2004) maximum acceptable limits of 10 μg l⁻¹ and 0.3 mg l⁻¹, for drinking water.     

Geochemical hazard evaluation of sulphide-rich iron mines: The Rio Marina district (Elba Island,Italy)

Rio Marina mining district (Elba Island) is characterised by hematite + pyrite ore association and was exploited for iron till 1981, leaving waste rock dumps of several millions m³. The effect of open pit mining activity in this site is to produce acid mine drainage (AMD) processes leading to environmental pollution, testified by all the sampled waters (Giove stream, drainage channels, superficial pools and settling basin) which have pH values ranging from 2.08 to 3.35 and heavy metal concentrations that reach 903.16 mg/l for Fe, 45.02 mg/l for Mn, 10.08 mg/l for Zn and 1.75 mg/l for Cu. In the present work a space and time related approach to geochemical hazard evaluation was applied. The geochemical hazard is mainly related to high heavy metal concentration, acid mine drainage processes development and topographic setting. As all these parameters are related in space, hazard evaluation was performed by geostatistical methods. Fifty-four earth material samples (residual soils, waste rocks or debris materials) were collected in a central aligned 100 m mesh square grid. These were analysed for major elements by XRF, for Cu, Pb, Zn by ICP-AES and for AMD potential following the AMIRA procedure. The concentration of heavy metals was compared with Italian law limits. The overlap of Cu, Pb and Zn content maps show that at least one of these heavy metals exceed law limits in all the area. The AMD test results show that more than 50% of samples have a positive NAPP (Net Acid Producing Potential) that could reach 258.9 kg H₂SO₄/t. According to the obtained data, three main geochemical hazard classes were established and their distribution in the mining area was assessed. About 51% of the mining area surface belongs to the major hazard class, where AMD process occurs, about 49% belongs to an intermediate hazard class, where AMD process could occur only if certain conditions are met. Finally, the persistence of the AMD process in the Rio Marina area was evaluated on the basis of yearly rainfall, mining waters pH and NAPP values. A complete leaching of the first 0.25 m of the earth materials can retain the current environmental conditions for several centuries.     

重庆秀山小茶园地区南华纪大塘坡组沉积环境与锰矿产出规律

在系统分析重庆秀山小茶园锰矿区大批钻孔数据资料的基础上,基于野外地质调查和室内沉积学、地球化学等分析得出,盆地中心相的沉积物厚度大,TOC、U、Mo、V、δ34S_py的含量高,草莓状黄铁矿丰富,指示了缺氧的水体条件,且锰矿的品位和厚度大。向盆地边缘相、斜坡相,沉积物厚度减小,TOC、U、Mo、V、δ34S_py含量降低,指示水体缺氧程度减弱,同时锰矿的品位和厚度减小。锰矿体厚度的变化与含锰岩系厚度的变化规律一致,二者呈正相关关系。小茶园矿区矿体展布方向与小茶园次级地堑盆地长轴方向基本一致,为NE60°左右。因此,小茶园矿区锰矿床矿体产出受到次级地堑盆地和沉积相带的控制,缺氧的盆地中心相成矿最佳,其次为盆地边缘相,斜坡相成矿较差。