Hydrothermal Gold Deposits Research Articles

The effects of mineralization on the lognormal distribution and exponential fluctuations of a hydrothermal gold deposit in Jiaodong Peninsula, China

Statistical analysis of the mineralization intensity in the No. І ore body of the Xincheng gold deposit in Jiaodong Peninsula, China, including grade and linear productivity, was used to study the mineralization characteristics of the hydrothermal gold deposit based on a lognormal distribution pattern and exponential fluctuations. The results show that the mineralization intensity of the hydrothermal gold deposit follows a lognormal distribution pattern. The grade and linear productivity in terms of the strike, dip, and thickness aspects are not linear, while the mineralization intensity fluctuations in exponential function were introduced between the peaks and valleys. This means the gold deposition mineralization process in the hydrothermal gold deposit takes place in accord with the mass action law of the first-order chemical reaction. The logarithmic averaging method is proposed to calculate the average grade and linear productivity of hypothermal gold deposits in accordance with the law of mineral fluctuations that are expressed as exponential functions. These research results have both academic and practical significance for further studies on hydrothermal gold mineralization, extra high-grade processing, improving traditional methods of estimation, and ultimately utilization of gold mineral reserves.

Application of geostatistical analyst methods in discovering concealed gold and pathfinder elements as geochemical anomalies related to ore mineralisation

Abstract The study area in the West Junggar Basin is known to be rich in hydrothermal gold deposits and occurrences, even though there has been minimum exploration in the area. It is here hypothesised that this area could host more gold deposits if mineral exploration methods were to be reinforced. This research is aimed at identifying geochemical anomalies of Au, and determining possible factors and conditions which facilitate the formation of anomalies by referring to As and Hg as gold pathfinders. Geostatistical analyst techniques have been applied to 9,852 stream sediments and bedrock data collected on a total surface of 1,280 km2 of West Junggar, Xinjiang (northwest China). The kriging interpolation and quantile-quantile plot methods, combined with statistical methods, successfully identified both Au and its pathfinders’ anomalies. In the present study, median was considered as background values (10.2 ppm for As, 9.13 ppb for Hg and 2.5 ppb for Au), whereas the 95th percentile were threshold values (28.03 ppm for As, 16.71 ppb for Hg and 8.2 ppb for Au) and values greater than thresholds are geochemical anomalies. Moreover, the high concentrations of these three discovered elements are caused primarily by hydrothermal ore mineralisation and are found to be controlled mainly by the Hatu and Sartohay faults of a northeast-southwesterly direction as well as their related secondary faults of variable orientation, which facilitate the easy flow of hydrothermal fluids towards the surface resulting in the formation of geochemical anomalies. Most of anomalies concentration of Au are found near the mining sites, which indicates that the formation of new Au anomalies is influenced by current or previous mining sites through geological or weathering processes. In addition, the low concentration of gold and its pathfinders found far from active gold mine or faults indicates that those anomalies are formed due to primary dispersion of hosting rock.

Chronology of the Kašperské Hory orogenic gold deposit, Bohemian Massif, Czech Republic

The Kasperske Hory deposit represents one of the economically most important hydrothermal gold deposits in the Bohemian Massif (Czech Republic). We present new Re–Os age determinations for sulfides complemented by Ar–Ar determinations on silicate minerals in order to provide temporal constraints on the deposit formation. Arsenopyrite and molybdenite formed during gold-bearing stages I–III yielded similar Re–Os ages between ~ 341 and 333 Ma, overlapping with the Ar–Ar cooling age of the metamorphic host rocks below ~ 500 °C. Continuous cooling of the ore system below 270 °C during stage III is reflected by Ar–Ar muscovite ages spanning from ~ 332 to 325 Ma representing the long interval of formation of gold-productive stage III. Thus, the Kasperske Hory gold deposit is younger than the gold deposits spatially associated with the Central Bohemian Plutonic Complex (~ 349–339 Ma) belonging to the Central Bohemian Metallogenetic Zone (e.g., Mokrsko-West, Jilove, Petrackova Hora). This may indicate a rather close relationship to the nearby Moldanubian Batholith while still suggesting an intimate link between mineralization and Variscan orogenesis and associated magmatism.

Morphology and chemistry of placer gold in the Bagrote and Dainter streams, northern Pakistan: Implications for provenance and exploration

The Bagrote and Dainter valleys in Gilgit Baltistan Pakistan, belonging to the Kohistan island arc and southwestern domain of the Karakorum metamorphic complex, respectively, are a location of regional placer gold mining. However, no in situ hydrothermal gold deposits have been discovered in this region. Here, we report the textural, morphological, and geochemical characteristics of placer gold from the stream sediments of the Bagrote and Dainter valleys with a view to trace the provenance. The morphological features of the studied gold grains indicate proximal source mineralization. The gold grains display a microtexture typical of mechanical abrasion rather than chemical activity. Their chemical composition of most of the grains from each stream falls in a restricted range (minor alloying elements mainly Cu) with high fineness (1,000 Au/(Au + Ag)), suggesting derivation from a homogeneous source or limited number of mineralization types. The high Cu content of the gold grains from the Bagrote stream suggests that the gold here might be associated with previously undiscovered porphyry gold mineralization, whereas the Au–Ag–Hg alloys from the Dainter stream suggest a genetic linkage with undiscovered fault‐controlled auriferous veins of epithermal origin in the southwestern part of the Karakorum metamorphic complex. The chemical composition of both streams placer gold in triangular diagram in terms of Au–Ag–Cu shows all the gold grains from Dainter stream were derived from epithermal type of mineralization, and most of the plots of Bagrote stream fall on the domain of porphyry epithermal type of deposits which are also in consistent with a continental arc setting in the study area. The mechanically developed microtexture, homogeneous chemical composition in individual grains from core to rim, and absence of high fineness rims of the gold grains from both streams, suggest the absence of any supergene regrowth and direct transfer from the primary source through glacier to the fluvial system. The Gilgit Baltistan province, dominated by dry temperate climate and glacial environment having steep geomorphology, precluding any significant supergene processes such as silver leaching and addition of authigenic gold on detrital gold grains.

Mineralogy of Bi-sulfosalts and tellurides from the Yaoan gold deposit, southwest China: Metallogenic implications

Bismuth-sulfosalts and -tellurides are commonly present in many hydrothermal gold deposits and can provide important genetic and physicochemical constraints on the metallogenesis. The abundant auriferous specular hematite veins in the Yaoan gold deposit of the Jinshajiang-Red River alkaline porphyry metallogenic belt (southwest China) contain an assemblage of Bi-sulfosalts and tellurides together with hematite, pyrite, and chalcopyrite. Bismuth-sulfosalts are characterized by replacement textures resulting from changes of fluid composition (e.g., Pb, Bi, Cu, and Ag) and mainly include bismuthinite derivatives (e.g., bismuthinite, paarite, krupkaite, lindströmite, and friedrichite-aikinite), paděraite, cuprobismutite homologues (probably submicroscopic intergrowths of hodrushite and cuprobismutite), and emplectite. Tellurides are tiny, comprising tsumoite, melonite, hessite, and calaverite, which coexist with bismuthinite derivatives. These Bi-sulfosalts and tellurides have direct contact with gold, indicating that the Yaoan gold metallogenesis was likely linked to the syenite porphyry magmatism that was originally sourced from a regional lithospheric mantle probably metasomatized by subduction of Te-rich sediments. The telluride assemblage also reveals that the gold was precipitated under oxidizing conditions that has a high tellurium fugacity at the beginning (fTe2 = ∼10−7.9 and fS2 = ∼10−8.5 at ∼300 °C).

Early Cretaceous Post-Collisional Collapse of the Yidun Terrane: Geochronological and Geochemical Constraints from Calc-alkaline to Alkaline Basalts in Xiqiu Area, Southwest China

Several Cretaceous Carlin-like or hydrothermal gold deposits along the Garze-Litang suture zone and Early Cretaceous hydrothermal copper mineralization along the southeastern margin of the Songpan-Garze fold belt were presumed to have a magmatic heat source. However, no actual coeval magmatic events nearby were discovered. Here, we report zircon SIMS U-Pb age, whole-rock geochemical and Sr-Nd isotopic data of the Xiqiu basalts in the southern end of the Yidun terrane, eastern Tibetan Plateau. New zircon U-Pb ages yield weighted mean 206Pb/238U age of 117.7±1.6 Ma. The basalts are classified as calc-alkaline to alkaline and have relatively high MgO (4.77 wt.%–10.84 wt.%) and Mg number values (Mg#=(100×Mg/(Mg+Fe2+)); 45.35–67.28) and positive eNd(t) (t=118 Ma) values (+1.86 to +3.2), suggesting a OIB-like mantle source that is consistent with the normalized patterns of trace elements and rare earth elements (REEs). Geochemical data suggest that the primary basaltic magma was generated by low degree partial melting of a peridotite-dominated mantle source with a minor component of garnet-eclogite or pyroxenite and experienced olivine+clinopyroxene dominated fractional crystallization. The primary melt compositions calculated from the high MgO samples, in turn, suggest that the Xiqiu basalts were generated at 1.6–2.9 GPa with abnormally hot mantle potential temperatures from 1 465 to 1 540 oC. The melting temperatures are similar to the abnormally hot mantle underneath the Colorado Plateau and hotter than the mid-ocean range basalt (MORB) mantle and normal intra-continental mantle. Combined with previous studies, the Cretaceous Xiqiu basalts allow us to reconstruct a tectonic and geodynamic evolutionary model responsible for the Late Jurassic to Late Cretaceous geological records (magmatism, ore deposits and enhanced exhumation) in the Yidun terrane and southern Songpan-Garze fold belt.

Gold deposits associated with the gabbroic rocks at Tirek area, western Hoggar, Algeria: fluid inclusion study

The Tirek gold deposit hosted in the Archean shield is one of the richest sources of mined gold for Algeria. The deposit is controlled by the East Ouzzal shear zone (EOSZ), a transcurrent N–S lithospheric fault. The EOSZ is a late Pan-African dextral-ductile shear zone separating two contrasting Precambrian domains: the Archean In Ouzzal block to the west (Orthogenesis with subordinate metasediments reworked and granulitized during the ca. 2 Ga Eburnean event) and a middle Proterozoic block to the east involved in the ca. 600 Ma Pan-African event. The auriferous quartz veins are mainly oriented in two directions, N–S veins hosted in mylonitic rocks and NE–SW veins hosted in gabbroic or gneissic bands. The NE–SW veins contain the richest ore. Gold ore is found in a system of veins and lenticular quartz veinlets arranged in anastomosing networks. The hydrothermal alteration associated with these veins is characteristically a carbonate-sericite-albite-pyrite assemblage. Gold is the main metal of economic importance; it is disseminated in the quartz as grains or fibers along microcracks and as microscopic grains in the host rocks. Microthermometric results and Raman laser data from fluid inclusions demonstrate that the ore-forming fluids contained H2O-CO2±CH4 and were low salinity. Homogenization temperatures are commonly 250–310 °C. In the Tirek deposit, the role of the shear zone that hosts the mineralization was to drain the hydrothermal fluid. Interactions between the fluid and the mafic host rocks and CO2 also contributed to the formation of the hydrothermal gold deposit at Tirek.

Origin and evolution of ore-forming fluids, and genesis of the Duhuangling and Jiusangou gold deposits in eastern Yanbian, northeast China

The Duhuangling and Jiusangou gold deposits are located east of the Yanbian area, northeast China. We present the results of systematic studies of the ore geology, fluid inclusion (FI) features, and isotopic geochemistry of the two gold deposits. Four mineralization stages have been defined in each gold deposit: pyrite + sericite + quartz (stage I), quartz + pyrite ± chalcopyrite ± arsenopyrite (stage II), quartz + native gold + polymetallic sulfide (stage III), and quartz–calcite (stage IV). FIs from the two gold deposits are similar and contain five types: pure vapor phase (V-type), vapor-rich phase (RV-type), liquid-rich phase (RL-type), daughter mineral-bearing polyphase (S-type), and pure liquid phase (L-type). Stage I FIs homogenize at temperatures of 350–450 °C, yielding salinities of 5.40–48.67 wt.%. FIs from both stages II and III samples homogenize at 160–350 °C, yielding salinities of 5.71–39.75 wt.%. FIs in pyrite from the stage II have 3He/4He ratios of 0.0069–0.0148 Ra and 40Ar/36Ar ratios of 1302–4433, demonstrating that ore-forming fluids of the two gold deposits were derived from the crust. The δD values of the two gold deposits range from −107‰ to −92‰, with δ18OH2O values from 4.3‰ to 9.0‰, indicating that the ore-forming fluids were mainly magmatic water in origin. Lead isotope data suggest that the ore-forming materials were originated from deep crust. Integrated data indicate that both Duhuangling and Jiusangou gold deposits are medium- to high-temperature, hydrothermal gold deposits.

Hydrothermal alteration and ore-forming fluids associated with gold-tellurium mineralization in the Dongping gold deposit, China

The Dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in China and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies. Pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit. The alteration minerals include orthoclase, microcline, perthite, quartz, sericite, epidote, calcite, hematite and pyrite, with the quartz, pyrite and hematite assemblages closely associated with gold mineralization. The phases of hydrothermal alteration include: (i) potassic alteration, (ii) potassic alteration - silicification, (iii) silicification - epidotization - hematitization, (iv) silicification - sericitization - pyritization and (v) carbonation. Mass-balance calculations in potassic altered and silicified rocks reveal the gain of K2O, Na2O, SiO2, HFSEs and transition elements (TEs) and the loss of REEs. Most major elements were affected by intense mineral reactions, and the REE patterns of the ore are consistent with those of the syenites. Gold, silver and tellurium show positive correlation and close association with silicification. Fluid inclusion homogenization temperatures in quartz veins range from 154°C to 382°C (peak at 275°C–325°C), with salinities of 4–9wt.% NaCl equiv. At temperatures of 325°C the fluid is estimated to have pH=3.70–5.86, log fO2=−32.4 to −28.1, with Au and Te transported as Au (HS)2− and Te22− complexes. The ore forming fluids evolved from high pH and fO2 at moderate temperatures into moderate-low pH, low fO2 and low temperature conditions. The fineness of the precipitated native gold and the contents of the oxide minerals (e.g., magnetite and hematite) decreased, followed by precipitation of Au- and Ag-bearing tellurides. The hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock-hosted hydrothermal gold deposit.

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Gold nuggets (centimetre scale) have formed in a supergene alteration zone on hydrothermal gold deposits, and occur intergrown with quartz and iron oxyhydroxide pseudomorphs after sulphide minerals, and along fractures in quartz and host rocks. The supergene alteration was driven by groundwater-driven water-rock interaction near to a regional unconformity beneath fluvial sediments, and involved clay alteration and oxidation that extended up to 50m below the unconformity. Oxidation of pyrite and arsenopyrite produced temporary thiosulphate ligands that mobilised microparticulate gold encapsulated in the sulphide minerals. The nuggets have some crystalline form, and internally they consist of anhedral grains, elongated gold plates, and intimate intergrowths of gold and iron oxyhydroxide. Nugget surfaces have further micron scale overgrowths of microparticulate gold, gold plates, and gold crystals. Nuggets were eroded and recycled into nearby proximal Miocene quartz pebble conglomerates, where they concentrated in placers near the basal unconformity. Later recycling transferred gold into Pleistocene fluvial channels. Gold dissolution and redeposition as plates and crystals occurred on the exterior surfaces of placer gold particles, with little change in mass. All groundwater maintained high pH throughout the geological history because there was sufficient calcite in the basement rocks to neutralise any acid generated by pyrite oxidation. Hence, gold mobility in sediments was driven by thiosulphate complexes as for the in situ nuggets, albeit with lower dissolved sulphur concentrations. Despite aridification of the climate in the late Cenozoic, with resulting localised high dissolved chloride concentrations, chloride complexation did not contribute to gold mobility.

Geological evolution and huge ore-forming belts in the core part of the Central Asian metallogenic region

The multi-stage geological evolution and extensive continental deformations during the course of its history make the Central Asian metallogenic region (CAMR) a unique and complicated large-scale metal domain. New geological observations and precise age-data allow an improved reconstruction of the geological evolution of the CAMR. This paper summarizes the Paleozoic orogenic evolution and related ore formation in the core part of the CAMR based on the geological data published both during the Soviet period and the last decades. Four ore-formation provinces (Altay, Balkhash-Junggar, Chu-Yili-Tianshan, and Southwest Tianshan) could be classified. The Balkhash-Junggar and Chu-Yili-Tianshan provinces are the major topics of this paper. The Balkhash-Junggar province consists of 4 huge ore-forming belts (Zharma-Saur, Tarbahtay-Xiemistay, Aktogay-Baerluke, Balkhashwestern Junggar) with 11 large ore-college areas. The Chu-Yili-Tianshan province consists of 4 huge ore-forming belts (Alatau-Sairimu, Chu-Yili-Bolehuole, Issyk-Awulale, Kazharman-Nalaty) with 22 large ore-college areas. Formation of large ore-college area corresponds to a specific stage of continental crust growth. Comparison of geology and ore deposits in the CAMR provides rich information for future exploration and understanding of ore-forming processes. The Paleo-Junggar Ocean closed at Early Devonian in the Balkhash-western Junggar ore-forming belt. Afterwards, widespread volcanicsedimentary rocks formed at extensional stage due to delamination of the thick lower crust formed during previous accretionary processes. Felsic magma intrusion caused formation of porphyry Cu-Au deposit at ∼310 Ma and related hydrothermal gold deposits about 10 Ma later. For example, in the Hatu-Baobei-Sartohay Au-Cr ore-college area in the Balkhash-western Junggar ore-forming belt, small granitic to diorite plutons and various dykes (312–277 Ma) and large granite bodies (∼300 Ma) intruded into the Devonian to Early Carboniferous volcano-sedimentary basin. These magmatic activities and fault systems mainly controlled ore-forming processes.

Te-Xe法による鉱化年代測定－熱水性金鉱床を例として－

Te-Xe法による鉱化年代測定－熱水性金鉱床を例として－

Multi-stage enrichment processes for large gold-bearing ore deposits

A review of previous studies of the world's large hydrothermal gold deposits indicates that the largest deposits tend to show complicated parageneses where multiple gold enrichment events and processes have been involved in the deposit generation. These observations suggest that multistage processes may even be a requirement for the formation of large deposits. In some deposits (e.g. Witwatersrand, Boddington Cadia, Sukhoi Log or Carlin) the different enrichment processes occur millions of years apart. In others, such as many large porphyry deposits, the different stages are much closer in time. In many deposits, particularly sedimentary-hosted deposits, early diffuse enrichment occurs within a particular province that is then upgraded by more focused processes (e.g., Sukhoi Log; Kalgoorlie). The presence of this early diffuse enrichment could explain the tendency for gold deposits to cluster into camps.This model has important implications, as the presence or absence of multiple gold events could be used to discriminate, at the exploration and feasibility stages, between small deposits with single stage ore genesis and more complicated deposits with multistage enrichment and the potential for larger gold endowment.

Microchemical signature of alluvial gold from two contrasting terrains in Cameroon

The microchemical signature of alluvial gold particles has wide application in constraining their primary sources. In this study, we apply this concept to investigate the composition of gold-bearing alloys from alluvial samples draining two geologically distinct terrains in southern and eastern Cameroon where the search for primary gold has remained elusive. The first set of gold grains (Lom grains) are from the Lom river drainage system with predominantly metasedimentary Pan-African rocks in the catchment region while the second set of grains (Nyong grains) are from the Mbal and Ebap tributaries of the Nyong river draining over a Paleoproterozoic complex comprising metamorphosed ultramafic rocks, amphibolites and granulitic gneisses. The gold grains recovered from these fluvial networks after panning were first studied under an electron microscope in order to evaluate their morphological features and subsequently embedded in epoxy resin, polished, and their compositions determined by both electron microprobe (EMPA) and laser ablation (LA-ICP-MS) techniques. The Lom grains are irregular to sub rounded with extensively pitted surfaces while the Nyong grains are predominantly rounded, oblong and with smooth surfaces. Nyong grains are devoid of inclusions while galena and pyrite are entombed in the Lom grains. Both set of grains are essentially Au–Ag alloys although the Ag content of the cores of the Nyong grains from both EMPA and LA-ICP-MS analytical techniques are significantly lower (0.05–6.07 wt% Ag; 93.54–99.29 wt% Au) than for Lom gold (0.06–22.75 wt% Ag; 78.76–99.86 wt% Au). X-ray element distribution maps do not show any zonal variation in core composition suggesting the gold grains derived from lode sources with single episode of hydrothermal gold deposition. Also the Nyong grains have significant amounts of Pt, Pd and Cr suggesting a link with ultramafic rocks while the Lom grains have substantial Sb and Zn levels pointing to hydrothermal quartz veining as the possible primary mineralization system. The grains from both localities have Ag-depleted rims. The results demonstrate that the microchemical signature of gold is useful to study the hypogene environment of a given area and a field for hydrothermal-orogenic gold is proposed on the ternary Au–Ag–Hg and Au–Ag–Cu plots.

Hydrothermal Gold Deposits in Pingle Depression: a Case Study at Gaocheng Quartz Vein‐hosted Gold Deposit

Hydrothermal Gold Deposits in Pingle Depression: a Case Study at Gaocheng Quartz Vein‐hosted Gold Deposit

Anomaly Geochemical Fields in Siberian Hydrothermal Gold Deposits

The composition and internal structure of geochemical fields associated to hydrothermal gold deposits within the Siberian territory were investigated. The concentric zonal structure of ore-forming geochemical fields embracing accumulations of Au, Ag, Bi, Pb, Zn, Cu, Te, As in ore bodies and their adjacent locations, and Ni, Co, V, Cr, Mn, Ba, Ti – within the external margin of gold ore formations were determined. The thermometric properties of gas-fluid inclusions in minerals of hydrothermal gold deposits were described. The results specified not only high-mineralized but also weakly-salted fluids are involved in the formation of the deposit. The latter is subjected to both retrogressive boiling and the mechanisms of direct and reverse osmosis. In this case, ascending and descending fluids produce eddy fluxes during Earth rotation, where minerals of different composition are formed in this flow path. Produced spiral mineral-geochemical fields can be observed on satellite images as hierarchy circular pattern system. Both the analysis of anomalous geochemical field structure and satellite images make it possible to predict the ore bodies of different grades in complicated landscape geological conditions.

A GIS-based weights-of-evidence model for mineral potential mapping of hydrothermal gold deposits in Torbat-e-Heydarieh area

The method of weights of evidence is one of the most important data-driven method for mineral potential mapping in GIS. In this method, considering the characteristics of known mineralized locations, new mineralized areas can be prospected. In this study, the method of weights of evidence was used for hydrothermal gold potential mapping in Torbat-e-Heydarieh area, east of Iran. As a relatively large number of gold mineral occurrences (i.e., exactly 27 known gold mineralized locations) have been recognized in the study area, the use of the weights of evidence method for prospecting new gold mineralized zones in the area can be quite efficient. To determine probable gold mineralization zones in the form of a posteriori map of the survey area, based on weights of evidence method, this study combined the results of the airborne geophysical, geological, argillic, propillitic and iron oxide alteration, geochemical and structural data were. Consequently, four major zones in this area were identified as high gold mineralization potential zones, in which many vein and veinlet mineralization forms can be found.

The Kiloton Class Jiaojia Gold Deposit in Eastern Shandong Province and Its Genesis

AbstractThe recent deep prospecting results in the Jiaojia area of Eastern Shandong Province indicate that the Jiaojia ore field composed of several individual gold deposits as previously suggested is actually an ultra‐large gold deposit. This deposit covers an area of ∼40 km2, and shows a structural control by the Jiaojia fault and its secondary faults. Gold orebodies generally occur along the same mineralization‐alteration belt, and the main orebodies intersect with each other or exhibit a parallel or overlapping distribution. This deposit's reserves are estimated to be 1, 200t of gold, being the first gold deposit of more than 1000t gold reserves in China. The No. I‐1 orebody in the Shaling‐deep Sizhuang ore blocks holds gold reserves greater than 350 t, or 29 percent of the total reserves, followed by the No. I orebody in Matang‐Jiaojia ore blocks with exceeding 150t gold reserves. This deposit mainly occurs in the footwall of the Jiaojia fault, and presents zoned patterns in mineralization, alteration and structures. The strongly mineralized zones agree with strongly altered and tectonically fractured zones. These orebodies display strataform‐like, veinlike or lenticular shapes, and generally show characteristics of pinching out and reappearing, branching and converging, expanding and shrinking. The orebodies commonly occur along positions where the fault strike changes and in gentle locations with dips changing from steep to gentle. The main orebodies are parallel to the main plane of the ore‐controlling fault, and tend to be gentle from the surface to the deep. The orebodies mainly plunge to the southwest, with plunge angle of 45°–60°. Orebodies near the main plane of the ore‐controlling fault have more gold resource than those away from main fault zone. The slant depth of orebodies is generally larger than the length along its strike direction; orebodies become thick and gold grades become low from the shallow area to the deep area. Ore‐forming fluids are H2O‐CO2‐NaCl±CH4 type with medium‐temperature and moderate to low salinity. Sulfur isotopic values (δ34SCDT) for gold ores range between 11.08‰ and 12.58‰, indicating mixed sulfur sources; hydrogen isotopic values (δDV‐SMOW) range from –83.68‰ to –116.95‰ and oxygen isotopic values (δ18OV‐SMOW) range between 12.04‰ and 16.28‰. The hydrogen and oxygen isotopes suggest that ore‐forming fluids originated from primary magma, and mixing with a large amount of atmospheric water during the late stage. The Eastern Shandong Province gold deposits are associated with magmatic activities which have mantle‐crust‐mixed source, and also share some similarities with orgenic and epithermal hydrothermal gold deposits. Because Eastern Shandong Province gold deposits with unique metallogenic features and formation setting which are different from other gold deposit types in the world, we call it the Jiaojia‐type gold deposits. The kiloton class Jiaojia gold deposit is related to fluid activities, extension and detachment resulted from thermal upwelling of magmas. The strong magmatic activities in the middle to late stage of early Cretaceous in Eastern Shandong Province lead to active fluids, and provided abundant ore‐forming materials for gold depsoits. Moreover, many extensional structures resulting from crustal extension provided favourable space for orebody positioning.

Analysis of relationship between belts of concentrated remote sensing linear structures and gold deposits as well as prospecting prognosis in Xiaoqinling region

Xiaoginling region has densely- distributed magama hydrothermal gold deposits. The structural framework in this region is the Neoarchean gneiss dome,where intense magmatic activities occurred in Yanshanian period. The gold deposits are closely related to the distribution of quartz veins and altered mylonite. In the ETM+remote sensing image,the deposits often find expression in linear,parallel linear intensive belts and flexible- brittle shear zones. Consequently,the distribution of remote sensing linear structures and the intensive belts of linear structures are very significant for the gold ore prediction in this region. On such a basis and with the ETM+remote sensing image as the basic map,the authors made interpretation of the linear structure intensive belts and circular structure of Yanshanian granite bodies in Xiaoginling region. The gold deposit distribution and metallogenic regularity were analyzed based on remote sensing interpretation,the maps showing the favorableness of the metallogenic remote sensing characteristic conditions for gold deposits in this region were compiled,and the remote sensing prospecting prediction of gold resources in this region was made. These results will provide some reference for the prospecting of gold deposits in Xiaoqinling region and the assessment of mineral resource potential in Henan Province.

Fuzzy logic modeling for hydrothermal gold mineralization mapping using geochemical, geological, ASTER imageries and other geo-data, a case study in Central Alborz, Iran

The study area is located ~50 km in the north of Tehran capital city, Iran, and is a part of central Alborz Mountain. The intrusive bodies aged post Eocene have intruded in the Eocene volcanic units causing hydrothermal alterations in these units. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images were used to map hydrothermal alteration zones. The propylitic, phyllic and argillic alteration and iron oxide minerals identified using Spectral Angle Mapper (SAM) method. Structural lineaments were extracted from ASTER images by applying automatic lineament extraction processes and visual interpretations. An exploration model was considered based on previous studies, and appropriate evidence maps were generated, weighted and reclassified. Ore Forming Potential (OFP) map was generated by applying Fuzzy SUM operator on alteration and Pb, Cu, Ag, and Au geochemical anomaly maps. Finally, Host rock, geological structures and OFP were combined using Fuzzy Gamma operator (γ ) to produce mineral prospectivity map. Eventually, the conceptual model discussed here, fairly demonstrated the known hydrothermal gold deposits in the study area and could be a source for future detailed explorations.