Geochemistry, mineral paragenesis and geothermal conditions of oreforming fluids from the Ain El Bey Cu–Fe deposit: potential occurrence of native gold and precious metal traces (North African orogenic belt, Northern Tunisia)

The Ain El Bey abandoned mine, in North-West Tunisia, fits into the geodynamic context of the European and African plate boundary. Ore deposit corresponds to veins and breccia of multiphase Cu–Fe-rich mineralization related to various hydrothermal fluid circulations. Petromineralogical studies indicate a rich mineral paragenesis with a minimum of seven mineralization phases and, at least, six pyrite generations. As is also the case for galena and native silver, native gold is observed for the first time as inclusion in quartz which opens up, thus, new perspectives for prospecting and evaluating the potential for noble metals associated with the mineralization. Scanning Electron Microscope--Energy Dispersive Spectroscopy and Transmission electron microscopy analyses show, in addition, a large incorporation of trace elements, including Ag and Au, in mineral structures such as fahlores(tetrahedrite-tennantite) and chalcopyrite ones. The mineral/mineral associations, used as geothermometers, gave estimated temperatures for the mineralizing fluids varying from 254 to 330 ℃ for phase Ⅲ, from 254 to 350 ℃ for phase Ⅳ, and from 200 to 300 ℃ for phases Ⅴ and Ⅵ. The seventh and last identified mineralization phase, marked by a deposit of native gold, reflects a drop in the mineralizing fluid’s temperature(< 200 ℃) compatible with boiling conditions. Such results open up perspectives for the development of precious metal research and the revaluation of the Cu–Fe ore deposit at the Ain El Bey abandoned mine, as well as at the surrounding areas fitting in the geodynamic framework of the Africa-Europe plate boundary.

Exploration of Potential Ore Deposits along the Cameroon Volcanic Line from Gravity and Magnetic Studies

A gravity and magnetic study has been carried out along the continental part of the Cameroon Volcanic Line (CVL), with the aim to explore the possibility of ore’s presence into the basement of this region. Different processing techniques have been applied, including the isostatic residual, the analytic signal and the Euler deconvolution to compute the Bouguer and magnetic anomalies. Following Euler solutions (result of Euler deconvolution) and the analytic signal results, four profiles crossing main structures on the isostatic residual have been used to enhance the structure of intrusions in the studied area. Despite the lack of constraints in the studied region, the results show that the basement is intruded by bodies of different density (2.57 g/cm3 to 2.87 g/cm3), different size and shape, with depths between 1 and 10 kilometers. These bodies have been interpreted as old rocks then as potential reservoirs of rare ores. In addition, volcanic rocks modeled have constituted potential reserves of other ores like graphite, sulfur, copper, iron.

Fluid Inclusion Geochemistry of Metallic Ore Deposits in the South- Central Sector of theDa Hinggan Mountains in China

Physicochemical parameters of mineralization such as temperature, pressure, salinity, density, composition and boiling of ore fluids as well as pH, Eh, fo2 and reducing parameter in theprocess of mineralization of major ore deposits in the study district have been obtained by the authors through systematic observation and determination of characteristics and phase changes of fluid inclusions at different temperatures and analysis of gaseous and liquid phase compositions of the inclusions, thus providing a scientific basis for the division of mineralization-alteration stages, types of mineral deposits and minerogenetic series and the deepening of the knowledge about the ore-forming processes and mechanisms of mineral deposits. It is indicated that the deposits of the same type have similar fluid inclusion geochemical features and physicochemical parameters though they belong to different minerogenetic series, while the compositions of inclusions are not conditioned by deposit types but closely related to the minerogenetic series of deposits.

Dynamics of Ore-Forming Processesof the Stratabound Skarn Copper Depositsof Tongling, Anhui Province

The skarn and ore bodies of the stratabound skarn copper deposits of Tongling, Anhui Province, are both controlled by definite stratigraphic horizons, and they are concordant with the strata. They occur as layers and layer-like bodies in permeable carbonate rocks of the Middle-Upper Carboniferous Huanglong and Chuanshan Formations which are underlain by impermeable shale or siliceous rocks of the Upper Devonian Wutong Formation. The authors study the dynamics of ore-forming processes of the ore deposits with the dynamic model of coupled transport and reaction, and the following results are obtained: The salinity gradient and flow rate of the ore-forming fluids can both promote the mixing and reaction of juvenile water and formation water, and the permeable strata are favourable sites for the intense transport-reaction of mixing and the formation of deposits. (2) As isothermal transport-reaction took place along the bedding of strata, the moving transport-reaction front formed at the contact between the ore-forming fluids and the rocks advanced slowly along the permeable strata, and then stratiform skarn and ore bodies concordant with the strata were formed. (3) The gradient transport-reaction taking place across the isotherms in the cross-bedding direction caused the mineralogical composition to alter gradually from magnesian skarn to sulphide ore bodies.

A Study of Occurrences of Ag in Pb-Zn-Cu Ore Deposits in China

A systematic study of occurrences of silver in 156 Pb-Zn-Cu ore deposits indicates that silver mainly occurs in nonferrous metal ore deposits in forms of association and paragenesis. It occurs mainly as independent minerals in nature and occasionally as ion adsorption, isomorphous or amorphous silver minerals. Nearly 190 silver minerals have been discovered in China. Their shapes, constituents, textures, grain sizes, embedded types, distribution patterns, mineral assemblages and metallogenic series suggest that these characteristics are closely related to geneses of deposits and dependent of ore-forming conditions. Pb, Zn and Cu sulphides are the main carrier minerals of silver. The partition of silver in ore is constrained by the mineralization intensity, grain size and embedded form of silver minerals and mineral assemblages.

Oxygen Isotope Studies of Wolframite in Tungsten Ore Deposits of South China

Based on the oxygen isotopic compositions of 133 wolframite samples and 110 quartz sampleseollected from 30 tungsten ore deposits in south China,in conjunction with δD values and other data,thesc deposits can be divided into four types. （l）Reequilibrated magmatic water-hydrothermal tungsten ore deposits. The δ18O values ofwolframite and quartz samples from this type of tungsten ore deposits are about +5-+12‰,respectively.The calculated δ（18）OH2O values of ore fluids in equilibrium with quartz are about+65‰,and the δDH2O values of fluid inclusions in quartz range from -40 to-70‰. （2）Meteoric water-hydrothermal tungsten ore deposits.Theδ18O values of wolframite in this type oftungsten dePosits are around-1‰. （3）Stratiform tungsten ore deposits.In these deposits,theδ18O values of quartz and wolframite areabout+17 and+3‰,respectively.It is considered that these stratiform tungsten ore deposits aregenetically related to submarine hot—spring activities。 （4）Complex mid-hydrothermal tungsten ore deposits.These tungsten ore deposits arecharacterized by multi-staged mineralization.The δ18O values of early wolframite are around+5‰,butof later wolframite are lower than+4‰,indicating that the early wolframite was precipitated fromreequilibrated magmatic water-hydrothermal solutions and the late one from the mixture ofhvdrothermal solutions with meteoric waters or mainly from meteoric waters, Based on the δ18O values of the coexisting quartz and wolframite and temperature data,twocalibration equilibrium curves have been constructed,and the corresponding equations have beenObtained: 1000 lnaQ-Wf=2.565×107T-2—7.28×l04T-1+57.27 1000 In aWf-H20=-2.285×107T-2+7.49×104T-1-61.79.

+-Evidence of Porphyry Deposits in the Ntem Complex: A Case Study from Structural and Hydrothermal Alteration Zones Mapping through Landsat-8 OLI, Aeromagnetic and Geological Data Integration in the Yaounde-Sangmelima Region (Southern Cameroon)

A semi-regional study was carried out in the Yaounde-Sangmelima area, a densely vegetated tropical region of southern Cameroon located in the Central Africa Fold Belt (CAFB)/Congo Craton (CC) transition zone. Towards structural lineaments and predictive hydrothermal porphyry deposits mapping, an integrated analysis of Landsat-8 OLI data, aeromagnetic, geological and mineral indices maps was performed. The Remote sensing using False colour composite images involving bands combinations and Crosta method (features oriented principal components analysis) enabled the mapping of the gneisses and schists domains without a clear differentiation between the Yaounde and Mbalmayo schists;despite the reflectance anomalies evidenced NW of Akonolinga, hydrothermal alterations in the study area failed to be detected. Besides, aeromagnetics depicted a moderately fractured northern zone (the CAFB) contrasting with a high densely fractured zone (the CC, known as Ntem complex). The Ntem complex displays signatures of a meta-igneous, an intrusive complex, greenstone relics south of Sangmelima and hydrothermal activity. Indeed, CET porphyry analysis tool detected many porphyry centres. In general, the study revealed many lineaments including contacts, fractures faults zones and strike-slips. The major aeromagnetics structures are SW-NE to WSW-ENE and WNW-ESE to NW-SE while those from Landsat-8 are NE-SW, WNW-ESE, NW-SE, WSW-ENE and NW-ESE to NNW-SSE. Together, these structures depict trans-compressions or trans-tensions corresponding to a broad NE-SW strike-slips channel that affect both the CAFB and the Ntem Complex, and they control the intrusions thus confirming a pervasive hydrothermal activity within the Ntem Complex. The proximity or coincidence of these porphyry centres with some mapped Iron-Gold affiliated mineral indices and porphyry granites indicate the possible occurrence of many hydrothermal ore deposits. These results show the high probability for the Ntem complex to host porphyry deposits so they may serve to boost mineral exploration in the Yaounde-Sangmelima region and in the entire southern Cameroon as well.

Magmatic Evolution and Mineralization of Porphyry Copper-Gold Deposits in the Duolong Ore Concentration Area, Tibet

The Bangong Lake-Nujiang River metallogenic belt is located between the Qiangtang Block and Lhasa Block, and the Duolong ore concentration area is located in the western section of the Bangong Lake-Nujiang River metallogenic belt. Till now, several large and super large copper-gold deposits, such as Duobuza, Bolong, Dibaonamugang, Naruo and Rongna deposits have been discovered in this area, mainly porphyry copper-gold ones.

The Mechanism of Structural Control of Ore Formation and Geochemical Characteristics in the Massive Sulfide Deposits of the Wushan Copper Ore Field,Jiangxi

The ore-controlling mechanism of the bedding fault system in the massive sulfide deposits of the Wushancopper orefield may be generalized as the control of ore deposition by optimum surface in an ore-formingstructural trap. The mechanism has three major features: (1) timing of mineralization; (2) positioning of hostformation; and (3) dependence of ore-controlling structure on properties of rocks. The 'optimum surface' is adivisional structural plane which marks obvious difference in physical, chemical and mechanical properties andis favorable for mineralization. It is also a unity of structures. lithofacies and orebodies. The structural and geochemical characteristics of the ore deposits indicate the migration trend of the ma-jor characteristic clements in the ore-controlling fault belt: elements with a small radius (Si, Fe, Mg and Al)moved towards and concentrated at the center of the belt while large-radius ones (Ca, K and Na) were remotefrom the center.

The Major Ore Clusters of Super-Large Iron Deposits in the World, Present Situation of Iron Resources in China, and Prospect

The metamorphosed sedimentary type of iron deposits（BIF） is the most important type of iron deposits in the world, and super-large iron ore clusters of this type include the Quadrilatero Ferrifero district and Carajas in Brazil, Hamersley in Australia, Kursk in Russia, Central Province of India and Anshan-Benxi in China. Subordinated types of iron deposits are magmatic, volcanic-hosted and sedimentary ones. This paper briefly introduces the geological characteristics of major super-large iron ore clusters in the world. The proven reserves of iron ores in China are relatively abundant, but they are mainly low-grade ores. Moreover, a considerate part of iron ores are difficult to utilize for their difficult ore dressing, deep burial or other reasons. Iron ore deposits are relatively concentrated in 11 metallogenic provinces（belts）, such as the Anshan-Benxi, eastern Hebei, Xichang-Central Yunnan Province and middle-lower reaches of Yangtze River. The main minerogenetic epoches vary widely from the Archean to Quaternary, and are mainly the Late Archean to Middle Proterozoic, Variscan, and Yanshanian periods. The main 7 genetic types of iron deposits in China are metamorphosed sedimentary type（BIF）, magmatic type, volcanic-hosted type, skarn type, hydrothermal type, sedimentary type and weathered leaching type. The iron-rich ores occur predominantly in the skarn and marine volcanic-hosted iron deposits, locally in the metamorphosed sedimentary type（BIF） as hydrothermal reformation products. The theory of minerogenetic series of mineral deposits and minerogenic models has applied in investigation and prospecting of iron ore deposits. A combination of deep analyses of aeromagnetic anomalies and geomagnetic anomalies, with gravity anomalies are an effective method to seeking large and deep-buried iron deposits. China has a relatively great oresearching potential of iron ores, especially for metamorphosed sedimentary, skarn, and marine volcanic-hosted iron deposits. For the lower guarantee degree of iron and steel industry, China should give a trading and open the foreign mining markets.

PRACTICAL AND PREDICTIVE MODELLING OF ORE DEPOSITS IN HYDROTHERMAL SYSTEMS

Over the pastfive years,we have been making efforts to develop a practical and predic- tive tool to exploreforgiantore deposits in hydrothermal systems. Towards this goal,a sig- nificant progress has been made towards a better understanding of the basic physical and chemical processes behind ore body formation and mineralization in hydrothermal systems. On the scientific developmentside,we have developed analytical solutions to answerthe fol- lowing scientific questions:(1) Can thepore- fluid pressure gradientbemaintained atthe val- ue of the lithostaticpressure gradientin the uppercrustof the Earth?and(2 ) Can convective pore- fluid flow take place in the uppercrustof the Earth ifthere is a fluid/mass leakage from the mantle to the upper crustof the Earth?On the modelling developmentside,we have developed numerical methods to model the following problems:(1) convective pore- fluid flow in two- dimensional hydrothermal systems;(2 ) coupled reactive pore- fluid flow and multiple species transport in porous media;(3) precipitation and dissolution of minerals and rock al- teration in the upper crust of the Earth;(4 ) double diffusion driven reactive flow transport in deformable fluid- saturated porous media with particular consideration of temperature- de- pendentchemical reaction rates;(5 ) pore- fluid flow patterns neargeological lenses in hydro- dynamic and hydrothermal systems;(6 ) dissipative structures for nonequilibrium chemical reactions in fluid- saturated porousmedia;(7) convectivepore- fluid flow and the related min- eralization in three- dimensional hydrothermal systems;(8) fluid- rock interaction problems associated with the rock alteration and metamorphic process in fluid- saturated hydrothermal/ sedimentary basins;and (9) various aspects of the fully coupled problem involving material deformation,pore- fluid flow,heattransferand species transport/ chemical reactionsin pore- fluid saturated porous rock masses. The above- mentioned work has significantly enriched our knowledge about the physical and chemical processes related to ore body formation and mineralization in the upper crustof the

Analysis of Mineralization System and Prediction of New-Type Ore Deposits

The discovery of new-type ore deposits, an important approach to guarantee the mineral resources supply in the 21st century, often brings about a gigantic increase in the mineral resources reserves. The analysis of mineralization system is of great importance to the discovery of new type ore deposits. ① The understanding of the relationship among various ore deposit types within a mineralization system in a region can help us to locate the unknown ore deposit types from the known ore deposit types, evidence that has been proved in the mineral prospecting history of ore belts in the middle and lower reaches of the Yangtze River, China. ② The understanding of the spatial structure of a mineralization system, especially of the vertical zonation, is helpful for the discovery of the concealed ore deposit types. ③ Clarifying the temporal structure of a mineralization system, including the iteration relationship between the mineral deposit types in the mineralization, leads to the location of the missing mineralization chains from the known mineralization chains (mineral deposit type), a method often proved to be effective in the magmatic hydrothermal mineralization system.④ Clarifying the factors restraining the diversity of mineral deposit types in mineralization system leads to the discovery of the potential of new type mineral deposits in relevant region. ⑤ Studying new mineralization setting and new ore forming processes leads to discovery of new type mineral deposit. More probabilities of discovery of new type mineral deposits are present in biogenic mineralization system, deep sea mineralization system, low temperature mineralization system, tectonic mineralization system and superimposed mineralization system.

Quantitative Prediction of Concentrated Regions of Large and Superlarge Deposits in China

Identification and quantitative prediction of large and superlarge mineral deposits of solid mineral resources using the mineral resource prediction theory and method with comprehensive information is carried out nationwide in China at a scale of 1∶5 000 000. Using deposit concentrated regions as the model units and concentrated mineralization anomaly regions as prediction units, the prediction is performed on GIS platform. The technical route and research method of locating large and superlarge mineral deposits and principle of compiling attribute table of independent variables and functional variables are proposed. Upon methodology study, the qualitative locating and quantitative predicting mineral deposits are carried out with quantitative theory Ⅲ and characteristic analysis, respectively, and the advantage and disadvantage of two methods are discussed. This research is significant for mineral resource prediction in ten provinces of western China.

Fuzzy Comprehensive Appraisal of Concealed Ore Deposits

In this paper, the transformation from the fuzzy to the accurate process is exemplified by the Jiaodong gold ore deposits concentrated region where the mathematical analysis is used to appraise and forecast regional concealed gold ore deposits. In this sense, this paper presents a new way to the appraisal of the non traditional mineral resources.

Geological Characteristics of Epithermal Ore Concentrated Areas and Epithermal Ore Deposits in China

The epithermal ore concentrated area is located in Southwestern China. We systematically study the regional geological characteristics such as the basement of Proterozoic, the capping bed, Moho, geothermal feature and tectonics, and discuss the relationship between distributed characteristics of the epithermal ore deposits and ore control factors in this paper. It is concluded that the conditions, under which the epithermal ore deposits form, are huge thick basement of Proterozoic, long time and wide scope developed capping bed and weak magmatic activity. The basement of Proterozoic that enriches volcanic matters and carbon and the carbonaceous bearing and paleo pool bearing capping bed provides main ore source. The large and deep faults and paleopool accordance with gravity anomaly gradient control the distribution of epithermal ore deposits. The lithologic assembles of microclastic rocks and carbonate rocks in the capping bed provide spaces of ore precipitation and create conditions of ore precipitation. The coincidence of many geological factors above forms the epithermal ore concentrated area.

Structural Origin of the Red-Ribbon Style Iron Ores in the Xinyu Iron Deposit,Central Jiangxi Province

The Xinyu iron deposit, located in central Jiangxi Province, is one of the most important BIF-type deposits in China. It is hosted in the Late Proterozoic volcanic- sedimentary rocks, which are composed of sericite- chlorite pyhllite, magnetite-bearing chlorite phyllite or schist, magnetite quartzite, and schist （Yu et al., 1989; Zeng et al., 2011）.