Geochemical and Spatial Appraisal of Fluoride in the Soils of Indo‐Gangetic Plains of India Using Multivariate Analysis

The geochemical characteristics and the spatial distribution of the fluoride were studied in the soils of Indo‐Gangetic plains using multivariate analysis. The fluoride (F) distribution in soil profiles and surface soil (0–15 cm) samples were studied. It was found that total fluoride (TF) in the profiles ranged from 248 to 786 mg kg^?1 with a mean of 515.1 mg kg^?1 whereas CaCl₂ extractable soluble fluoride (F_Ca) was found to be in the range of 1.68 to 99.1 mg F kg^?1 soil. On the other hand, in surface soils, the TF and F_Ca ranged from 118 to 436 mg kg^?1 with a mean of 251.2 mg kg^?1 and 1.01 to 5.05 mg kg^?1 with a mean of 2.12 mg kg^?1, respectively, in the study area. The principal component analysis revealed that the natural weathering of fluoride bearing rock and minerals, various ion‐exchange and dissolution processes in the soil, alkalinity, sodium adsorption ratio, calcium (Ca), magnesium (Mg), and clay contents of the soil are responsible for high fluoride occurrence in the area. The fluoride contamination index developed by using these factors could explain more than 76% variance of F contamination due to F_Ca in soils. The interpolated kriged map of F_Ca in surface soil indicated a distinct loop of 1.0–2.0, 2.0–3.0, 3.0–4.0, and >4.0 mg kg^?1.     

Mineral constituents in common chanterelles and soils collected from a high mountain and lowland sites in Poland

This paper reported the results of the determination of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr and Zn in Common Chanterelles (Cantharellus cibarius) Fr. and surface soil layer (0-10 cm) underneath the fruiting bodies. Mushrooms and soils were collected from a lowland site in the Hel Peninsula (Baltic Sea coast) and a high mountain site in the Tatra Mountains. The trace elements were determined using validated method and inductively coupled plasma - atomic emission spectroscopy (ICP-AES). Common Chanterelles that emerged at sites poor in mineral nutrients podzols of the Hel Peninsula forests efficiently bioconcentrated several essential trace elements (K, P, Co, Cu, Mn, Na, Zn), while the abundance of those elements in carpophores was around half less compared to specimens from Zakopane region and which emerged in soils much richer in minerals. Common Chanterelles collected at two spatially distant background areas in Poland were only weakly contaminated with metals such as Ag, Cd, Hg and Pb. The maximum tolerable Cd and Pb contents of certain cultivated mushrooms are regulated in the European Union by law and these hazardous metals in C. cibarius were far below tolerance limits set.     

Effects of misclassification costs on mapping mineral prospectivity

Mineral prospectivity mapping is a classification process because in a given study area, a specific region is classified as either a prospective or non-prospective area. The cost of false negative errors differs from the cost of false positive errors because false positive errors lead to wasting much more financial and material resources, whereas false negative errors result in the loss of mineral deposits. Traditional machine learning algorithms using for mapping mineral prospectivity are aimed to minimize classification errors and ignore the cost-sensitive effects. In this study, the effects of misclassification costs on mapping mineral prospectivity are explored. The cost-sensitive neural network (CSNN) for minimizing misclassification costs is applied to map Fe polymetallic prospectivity in China’s southwestern Fujian metalorganic belt (SFMB). A CSNN with a different cost ratio ranging from 1:10 to 10:1 was used to represent various misclassification costs. The cross-validation results indicated a lower misclassification cost compared to traditional neural networks through a threshold-moving based CSNN. The CSNN’s predictive results were compared to those of a traditional neural network, and the results demonstrate that the CSNN method is useful for mapping mineral prospectivity. The targets can be used to further explore undiscovered deposits in the study area.     

Delineation of potential exploration targets based on 3D geological modeling: A case study from the Laoangou Pb-Zn-Ag polymetallic ore deposit,China

The Laoangou Pb-Zn-Ag polymetallic ore deposit (LAG) is a hydrothermal vein-type deposit in the East Qinling polymetallic metallogenic belt, which is controlled by NW-, NE- and nearly SN-trending faults and mainly hosted in the dolomite marble of Meiyaogou and Baishugou formations within the Luanchuan ore district (LOD). Although district-scale metallogenic prediction related to the Pb-Zn-Ag deposits in the LOD has been attempted, there have been no studies to formulate a detailed deposit-scale metallogenic prediction of the Pb-Zn-Ag deposit in 3D space. Here we selected the LAG to formulate a metallogenic prediction model for Pb-Zn-Ag deposit based on data from 1:10,000 scale geological map, and 66 boreholes and 39 sections of exploration lines on 1:1000 scale, to extract the salient spatial features of the deposit. We apply ordinary weights and weighted weights of evidence, followed by boosted weights of evidence, logistic regression and information entropy for integrating the features of the ore deposit for exploration targeting. The C–V fractal method is applied to classify the probabilities. Accordingly, three levels of exploration targets are delineated: the first level targets are mainly distributed in the periphery of known orebodies (M2, M3, II-3 and VI), which are also located in the ore-controlling strata and fault zones; the second level targets are located in the region of known orebodies, indirectly confirming that the prediction result is reliable; and the third level targets, which are mainly located at the contact between ore-controlling strata and metagabbro bodies, offer new targets for exploration in this ore district. Combining our results obtained in this study with those in previous studies, we provide some guidelines for exploration targets in the Pb-Zn-Ag deposits in the LOD, which might help in more effectively delineating the target zones.     

The rare earth element (REE) mineralisation potential of highly fractionated rhyolites: A potential low-grade,bulk tonnage source of critical metals

The rare earth elements (REE) have become crucial for modern industry, technology and medicine, with the increase in demand for these elements over the past few years currently being met by relatively few well-known mineral deposits. This lack of a secure supply of the REE has led to increased research into potential alternative sources of these in demand elements. The primary fractionation processes involved in the petrogenesis of highly fractionated high-silica rhyolites can cause the magmas that form these units to become preferentially enriched in the REE, especially in the more valuable heavy REE (HREE), although this is dependent on the mineral assemblages fractionated by the system in question, a factor that is in turn a function of the source and tectonic setting of a given magmatic event. The mineralogy of the REE is also important, with volatile exsolution and vapour-phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the REE and other elements into concentrations (and more importantly potentially acid leachable and therefore processable minerals) that may be economically viable to extract. This, combined with the fact these rhyolites are often enriched in other critical and/or economically important metals (e.g., Y, Nb, Ta, Be, Li, F, Sn, Rb, Th, and U) means that these volcanic units should be considered as potential sources of these critical metals. In addition, the large volume nature of these rhyolites combined with the fact they frequently crop out at the Earth’s surface makes them ideally suited for more economical bulk open pit extraction. This suggests that these high-silica REE-enriched rhyolites should be considered potential REE analogues of bulk-tonnage, low-grade porphyry Cu deposits, warranting further investigation to determine whether these rhyolites are a viable new source of the REE (especially the HREE) and are potential targets for future mineral exploration.     

Geochronological and mineralogical constraints on mineralization of the Hetai goldfield in Guangdong Province,South China

The Hetai goldfield, located in the southern segment of the Qinzhou Bay-Hangzhou Bay Juncture Orogenic Belt (QHJB), is the largest concentration of gold deposits in Guangdong Province, South China. The gold mineralization is hosted within the late Neoproterozoic to early Paleozoic Yunkai Group and strictly confined to mylonite (ductile shear) zones. The nature of the structural control of mineralization, in particular the role of ductile versus brittle deformation and their ages, which remain unclear despite numerous previous studies, are examined in this paper through an integrated study of geochronology and mineralogy.Lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism, but the majority of the ores are associated with brittle deformation features. In combination with macroscopic and microscopy observations on shear fabrics, LA-ICP-MS U-Pb dating on zircons of hydrothermal origin from mylonites suggests that the Hetai goldfield was subjected to two shearing events: an early sinistral ductile shearing at ca. 240 Ma, and a late dextral ductile-brittle shearing at ca. 204 Ma (Indosinian). These ages are ca. 90–30 Ma older than the previously published gold mineralizing ages of ca. 175–152 Ma (Yanshanian), suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation. This inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite (ca. 350–290 °C), chlorite (ca. 260–230 °C), and sphalerite (ca. 230–170 °C) intergrown with native gold, which are considerably lower than that for the ductile deformation (500–300 °C or higher). Based on these data, we propose that the gold mineralization in the Hetai goldfield predominantly occurred during the Yanshanian event, and only minor gold mineralization and associated sulfidation took place during the earlier Indosinian ductile deformation.     

A prediction model for important mineral resources in China

Prediction models for mineral resources provide an analytical foundation and method to express the results of resource evaluations. The project “China National Mineral Resources Assessment Initiative” was conducted during 2006–2013, with the aim to determine the location, quantity, and quality of 25 important mineral resources occurring at depths of <1 km. There are currently 80 integrated prediction models on the scale of III–level metallogenic belts in use across China. The Huangshaping Pb–Zn polymetallic deposit, Hunan province, China, is used as a case study to establish methods and processes for developing a mineral resource prediction model that would be used for exploration targeting. The construction of prediction models requires the development of a classification scheme for the proposed prediction method appropriate for the prediction area. An initial metallogenic model is quantitatively transformed to a prospecting model, and then a prediction model. The incorporation of additional methodology, analysis of a comprehensive geological database, and correlation of asymmetric information between the well–explored typical deposit area and regional prediction area, yield an integrated prediction model. This paper also discusses the prediction modeling theory, and presents 12 models used for mineral assessments.     

证据权模型与含矿网格单元蒙特卡洛法相结合的资源潜力评价新方法

本文提出了计算含矿单元数概率分布函数的新方法,在此基础上,把证据权模型矿产资源评价方法得到的含矿网格单元作为蒙特卡洛模型中的统计对象,得到了与证据权模型找矿法结合的含矿网格单元蒙特卡洛法矿产资源潜力评价方法。该方法可以把评价工作区的矿产空间分布信息、成矿模式和找矿模型、成矿-找矿空间信息引入蒙特卡洛方法中,无需估计矿床个数分布,减少了工作步骤和评价误差,可提高工作效率和自动化。对实际案例的应用表明该方法是可行的。     

赣杭构造带灵山花岗岩体黑云母的矿物化学特征及其对岩石成因的指示意义

灵山花岗岩体在平面上为一环状分布的侵入体,中心为角闪石黑云母花岗岩,外围为黑云母花岗岩。在角闪石黑云母花岗岩中分布有大量的暗色镁铁质微粒包体。黑云母是大多数中酸性火成岩中比较重要的一种镁铁质矿物,它能很好地反映寄主岩浆的属性和成岩时的物理、化学条件,因此,本文对这两种花岗岩及镁铁质微粒包体中的黑云母开展了系统的岩相学观察和电子探针化学组成研究,探讨灵山岩体的物质来源、成岩条件和岩浆的混合作用过程。研究结果表明两种花岗岩体的黑云母具有不同化学成分,而暗色镁铁质微粒包体中黑云母的化学成分则变化较大。三种黑云母均在低氧逸度条件下晶出。两种花岗岩中的黑云母均富Fe贫Mg,属于铁质黑云母,含铁系数[(Fe~(3+)+Fe~(2+))/(Fe~(3+)+Fe~(2+)+Mg~(2+))]分别为0.65~0.70,0.72~0.78,FeOT/MgO均接近7.04。MF值[2×Mg/(Fe~(2+)+Mg+Mn)]分别为0.64~0.76和0.48~0.60,指示两种花岗岩的物质来源都是以壳源为主。镁铁质微粒包体中黑云母的MF值变化范围比较大,为0.63~1.06,为铁质黑云母到镁质黑云母,暗示包体岩浆经历过不同程度的岩浆混合作用。镁铁质微粒包体中部分黑云母与角闪石黑云母花岗岩中黑云母的结晶条件相似,而部分则有明显差异,推测是由于基性的镁铁质包体岩浆注入到酸性的花岗岩浆是一个连续多阶段的过程。     

胶西北中生代花岗岩中黑云母和角闪石成分特征及成岩成矿意义

在详细的野外地质和岩相学观察基础上,对胶西北中生代玲珑期、郭家岭期和伟德山期花岗岩中的黑云母和角闪石进行了系统的化学成分研究。结果显示,玲珑期,研究区中部和南部花岗岩中的黑云母为铁叶云母和铁质黑云母,其MgO为4.07%~6.53%,具有壳源型黑云母的特征;北部主要为铁质黑云母和镁质黑云母,MgO介于9.13%~11.57%之间,具壳幔混源型的特征;郭家岭期和伟德山期花岗岩中的黑云母以铁质黑云母和镁质黑云母为主,MgO为7.62%~15.38%,均为壳幔混源型,其中的角闪石均属于钙质角闪石,M值为0.44~0.76。暗色矿物成分显示玲珑期花岗岩的源区物质主要为壳源,郭家岭期和伟德山期的以壳源为主,有少量幔源组分参与。三期花岗岩中黑云母结晶温度主要集中于550~700℃,而角闪石的结晶温度为600~750℃,从玲珑期到郭家岭期再到伟德山期,即从早到晚,黑云母的结晶温度有升高的趋势;全铝压力计估算结果显示,黑云母和角闪石的结晶压力具有降低的趋势。郭家岭期和伟德山期花岗岩中黑云母结晶过程中的氧逸度分别为-15.0~-9.0和-15.3~-8.8,明显比玲珑期的(-17.5~-13.2)高。结合胶西北金矿的时空分布特征,认为花岗岩结晶过程中较高的氧逸度和幔源物质的参与可能是有利于金矿化的重要条件之一。