Thallium in the Carlin-type gold deposits

Five Carlin-type sediment-hosted precious metals deposits from the western United States have been analyzed for Tl, Rb, K, Sr, Au, and Ag, and the relationship between Tl, Rb, and K in mineralized and unmineralized rocks has been studied. The Carlin-type gold deposits studied include Carlin, Alligator Ridge, and Jerritt Canyon deposits of Nevada, Mercur deposit of Utah, and North Moccassin deposits of Montana.The mineralized rocks of all five deposits contain significantly high contents of Tl and low K/Tl and high Tl/Sr ratios. The oxidized mineralized rocks of the Carlin and Mercur deposits have higher contents of Tl than carbonaceous rocks while siliceous rocks from most of the deposits contain the lowest Tl concentrations.The K/Tl ratio and the relationship between Tl, Rb, and K can be used to separate mineralized and unmineralized rocks into two distinct populations in order to outline, successfully, potential mineralized areas. The data presented in this paper suggest that Tl is probably a more useful indicator element than Au and other associated elements, at least under certain situations.     

锌同位素在矿床学中的应用：认识与进展

文章报道了安徽铜陵新桥和凤凰山矽卡岩型矿床中闪锌矿和共生黄铁矿间的Zn同位素组成,获得了锌同位素在这2个矿物间的分馏系数,系统总结了锌同位素在不同储库和不同类型矿床中的分布特征,结合最新的研究成果,较全面地总结了锌同位素在矿床学领域的应用,得出了锌同位素可以用来示踪流体演化和源区变化的基本认识。在成矿流体体系的演化过程中,随着矿物的沉淀,流体的逐渐富集重同位素,晚期矿物相对于早期矿物富集锌的重同位素。在热液流体对同一源区淋滤萃取的过程中,重同位素优先被淋滤出来,晚期淋滤出的流体相对早期淋滤出的流体富集轻同位素。     

A review of mineral resources in Malawi: With special reference to aluminium variation in mineral deposits

The lithology of Malawi is characterized by Precambrian metamorphic and igneous rocks which form part of the polyphase East African Orogen. Rift-related sedimentation and igneous activity during the late Paleozoic (Karoo System) and the late Mesozoic (Chilwa Province) have produced a great variety of rocks that underwent strong chemical weathering and erosion when the entire region received its final shape by peneplanation and fluvial incision during the Cenozoic under (sub)tropical climatic conditions. Aluminum is a dominating element in minerals (e.g., corundum, kyanite, beryl, gibbsite) in this region. Some minerals were concentrated in deposits bound to Al-enriched host rocks (zircon, pyrochlore, eudialyte, uranium minerals) with high A/CNK ratios, whereas others, e.g., asbestos, chalcedony, monazite, kaolinite, ilmenite and garnet have host rocks of a low A/CNK ratio. Aluminum was used to categorize these various mineral deposits. The abundance of aluminum and accumulations of Nb, Zr, Ti, REE, Sr and Ba point for some mineralisations to similar subcrustal carbonatite-forming systems that were operative during periods of the Precambrian and the Mesozoic in Malawi. Aluminum variation does not only reflect differentiation in the various igneous rock series but it is also visible in the sedimentary realm during transport and weathering. In context with other elements such as Ti and P, Al provides an opportunity to reveal chemical relationships between rocks and mineral deposits. Spinel and Al-enriched silicate minerals can be used as pathfinder minerals in the stream sediments to guide the exploration geologist to non-metallic deposits.     

Metallic mineral deposits

Except for the fringing reef, the limestones of Christmas Island in the Indian Ocean are of Late Eocene (Tertiary “b") and Early Miocene (Tertiary “e” to “f") age. The Upper Eocene limestone is an algal limestone containing Discocyclina, Nummulites, and Heterostegina. The Lower Miocene limestone is an algal limestone containing in its lower part species of Lepidocyclina (Eulepidina) followed by Miogypsinoides dehaarti. Miogypsinoides dehaarti extends into the zone of Flosculinella bontangensis. No rocks younger than Burdigalian were identified other than on the fringing reef which contains an assemblage of Pliocene‐Pleistocene Foraminifera.     

Thallium in Low Temperature Ore Deposits,China

is paper deals with thallium in typical low-temperature deposits of Au,Tl,As,Sb and Hg in South China with respect to its mode of occurrence,minerals and geochemical correlations with many other coexisting major and trace elements,Criteria are proposed for identifying independent thallium deposits and thallium-bearing deposits and the Nanhnu realgar deposit is classified for the first time as an independent thallium deposit,Tl,F.Cl.I and B are suggested as indicators for low-temperature mineralization with examples furnished for their applications.     

华北地区镍矿床特征及资源潜力

华北地区镍矿床(点)主要分布在内蒙古、河北省及河南省等地,已发现镍矿床(点)19处,其中大型矿床1处,中型矿床3处,小型矿床8处,矿点7处.新元古代和晚古生代是华北地区镍矿床形成的2个高峰期.矿床类型以岩浆型为主,其次为风化壳型和沉积变质型.沉积变质型镍矿床主要产在华北陆块区内,形成环境与裂陷盆地有关;岩浆型和风化壳型...     

八论矿床的成矿系列

矿床的成矿系列(简称成矿系列)是区域成矿研究的一种学术思想,亦是地球系统四维成矿论.认为地球的矿床世界是由特定的时空域内,各类地质成矿作用形成的矿床类型组合的矿床自然体矿床成矿系列及其联合体成矿体系所组成.矿床形成决定于时间、空间、成矿作用三要素.矿床世界的基本单元是矿床成矿系列.矿床成矿系列组成成矿体系,成矿体系组成...     

A practical methodology to optimise marginal mineral deposits using switching real options

Currently depressed commodity prices have rendered many mining projects marginal irrespective of their geological merit. Tight capital markets discourage investment in their development because of their unappealing deterministic NPVs, which in the majority of cases reflect conceptual designs focused on achieving primarily economies of scale often at the expenses of operating flexibility. Given that project profits and cash flows are highly sensitive to movements in volatile commodity prices, circumstances now call for a re-direction of emphasis towards creating managerial flexibility to facilitate and minimize the cost of temporarily placing projects in care and maintenance and re-opening them in response to increases in prices. This flexibility, that is to say the option to alternatively switch the project between an open and closed state, can be created through an appropriate combination of mine design, commercial procurement arrangements and mode of operations that enables managers to anticipate and take advantage of future hikes in prices, while minimizing the negative effect of downturns. This paper presents a practical example of how to estimate the real option value (ROV) of this type of switching option, which is generally not captured by the deterministic DCF/NPV of projects. To facilitate the numerical presentation, initially the binomial lattice method is applied only to the first 2 years of a realistic DCF model of a gold mine, with an expected life of 5 years and a negative deterministic NPV. The model is limited to assessing the ROV created by introducing switching flexibility as a result of the volatility of the gold price in isolation. A consistent ROV is then obtained using as an alternative the unrelated decision tree methodology. This result is considered important as using decision trees for this type of analyses in cases where more than one source of uncertainty is involved (e.g. that of grades, costs, and exchange rates) does not require, as in the case of binomial lattices, estimating the volatility of a project cash flow. This process, which may create computational ambiguity and possible bias, can be avoided in decision trees as each source of uncertainty is represented by an individual event node. Finally the ROV of the project, including the switching option, is calculated over its whole 5-year life to provide some indication of the amount that could justifiably be invested up-front to create the necessary switching flexibility.     

Stochastic modelling of mineral deposits

Mineral deposits are characterized by certain continuity of assay values, thickness and top and bottom surfaces of ore zones etc., which are amenable to stochastic modelling with respect to spatial coordinates. The French School (Matheron, 1963) introduced rather difficult terminology of semi-variogram, kriging etc. for quantitative assessment of reserves and average grade of mining property under the assumption of second-order stationarity of first differenced (d=1) data. A more general, powerful and well-known time-domain (spatial) stochastic models (ARIMA (p, d, q); based on Box and Jenkins, 1970, 1976; Anderson, 1976) are introduced herein which include Matheron Model (d=1) as a special case.     

中国锡矿床时空分布特征与潜力评价

锡矿是中国传统优势矿种,但是近年来遇到了找矿潜力区不足和找矿方向不明等问题,急需进一步分析和总结其地质特征、成矿规律和资源潜力,为今后地质找矿工作提供借鉴。文中采用矿床模型综合地质信息预测方法,在各省区锡矿资源潜力预测成果的基础上,以MapGIS为平台,进行数据库汇总与综合分析研究。首先,基于全国893处锡矿产地数据的统计分析,初步总结了中国锡矿时空分布特征,岩浆岩、构造和地层等控矿因素。其次,根据锡矿床及预测区的空间分布和大地构造单元,划分了44个锡矿成矿区带。再次,将锡矿的预测类型划分为石英脉型、锡石硫化物型、夕卡岩型、云英型、伟晶岩型、火山岩型和砂矿型,并建立了主要锡矿类型的预测模型。最后,在全国范围累计圈定1 179个最小预测区,累计预测资源量1 861.13×104 t。根据锡矿区域成矿特征,将最小预测区归并为405个二级预测区,并进一步合并为109个锡矿三级预测区,其中找矿潜力大的湖南香花岭-千里山和塔山-大义山、云南个旧和薄竹山-都龙、内蒙古黄冈梁等5个三级预测区可优先部署锡矿勘查工作。预测结果还表明锡矿在500 m以浅的找矿空间里仍有很大资源潜力,因此,找矿工作应注重深浅结合,在重视老矿山深部外围找矿的同时,还应重视覆盖区和非传统锡矿类型等新领域的找矿勘查。     

Microbiological exploration for mineral deposits: a new technique

The measurement of metal resistance in microorganisms is a cost-effective technique that should be used to supplement the presently employed inorganic geochemical methods of exploration. The method is based on the measurement of metal tolerances in the total microbial population by means of the use of culture techniques. It is strongly recommended that the culture technique demonstrated here be integrated into reconnaissance exploration programs that require efficient focusing to be successful. The technique was developed and successfully tested in the Tomichi Mining District, Colorado, U.S.A., where the environment is subalpine to tundra and the metals sought include Cu, Pb, Zn, Ag, and Au. It is easily adapted to most environments and metals, and draws additional advantage from being able to detect mineralization at greater distance and with lower sample density than standard inorganic sampling techniques.     

Prospector II: Towards a knowledge base for mineral deposits

What began in the mid-seventies as a research effort in designing an expert system to aid geologists in exploring for hidden mineral deposits has in the late eighties become a full-sized knowledge-based system to aid geologists in conducting regional mineral resource assessments. Prospector II, the successor to Prospector, is interactive-graphics oriented, flexible in its representation of mineral deposit models, and suited to regional mineral resource assessment. In Prospector II, the geologist enters the findings for an area, selects the deposit models or examples of mineral deposits for consideration, and the program compares the findings with the models or the examples selected, noting the similarities, differences, and missing information. The models or the examples selected are ranked according to scores that are based on the comparisons with the findings. Findings can be reassessed and the process repeated if necessary. The results provide the geologist with a rationale for identifying those mineral deposit types that the geology of an area permits. In future, Prospector II can assist in the creation of new models used in regional mineral resource assessment and in striving toward an ultimate classification of mineral deposits.     

Italian ore/mineral deposits related to emersion surfaces a summary

Depositions of ores and/or industrial minerals below and/or along and above emersion surfaces (E. S.) are rather common in Italy, especially in carbonatic country rocks. The following materials are involved: Pb, Zn, Fe ox, Cu, Sb, Hg, Ag, U, Th, FeS₂, BaSO₄, CaF₂, Bauxite, Magnesite, Kaolin. The deposits are strictly connected to different sedimentary processes: pedogenesis, sedimentation and resedimentation (either normal or intra-karstic), supergene enrichment. Their shapes, according to the different processes mentioned above and to the position relative to the E. S., are: pipes, pockets, channels, discordant and/or interbedded lenses, crusts. The main examples are located in connection with the Cambro-Ordovician and the Devonian-Carboniferous unconformities, the Hercynian peneplane, the E. S. of Trias, of Cretaceous-Eocene, of Quaternary.