浅淡石英脉型金矿的采样方法

金矿采样方法十分重要。根据金品位在含金石英脉厚度方向上呈跳跃式的“W”型的变化规律来指,导金矿采样,能有效地提高采样质量,提高找矿效果。     

Geochemical signature of orogenic hydrothermal activity in an active tectonic intersection zone,Alpine Fault,New Zealand

A highly faulted and fractured rock mass has developed at the intersection of the Alpine and Hope faults, two major active faults in the South Island, New Zealand. The Alpine Fault is an oblique dextral reverse fault at the late Cenozoic-Recent Pacific-Australian plate boundary. The Hope Fault is a strike-slip fault parallel to the plate convergence vector. Hydrothermal fluids driven by the active tectonic processes have passed through the fractured rock mass, causing localised rock alteration and vein formation. Mylonites in the Alpine Fault zone are crosscut by cm-scale veins of quartz and/or ankerite with minor sulphides, with cemented breccias in dilational jogs. Breccia clasts and immediate (cm-scale) host rocks have been variably impregnated with carbonates and quartz. This generation of veins, breccias and altered rocks is post-dated by cataclasite and fault gouge zones which have been cemented by calcite, illite, smectite and chamosite. Ankerite and calcite have ¹⁸O between +10 and +30, and ¹³C between 0 and –8. These minerals are inferred to have formed from water with variable components of both meteoric and crustally exchanged fluid. Rock alteration associated with ankerite–quartz veins has added arsenic (up to 200 ppm As), strontium, and some Y to the rocks. Host-rock mylonites (<2 ppm As) have been depleted in arsenic compared to their precursors (5–15 ppm As). This depletion of arsenic in the middle crust provides the source for arsenic in shallower-level vein systems.Editorial handling: N. White     

Multiple Identities and Representations: Experiences in the Study of People's Life-worlds in Rural Malawi

This paper argues that in generating perceptual meanings of social actors as data, researchers need to deal with multiple representations, identities and categorisations of their own and those of their informants. The need to also consider power dynamics that develop in the communication process between the “researcher” and the "researched" in the process of generating data is also emphasised. The paper suggests that an analysis of image‐conflicts can be used to reveal the “hidden meanings” during these research encounters and improve the quality of research findings.     

IMU/DGPS supported photogrammetry in China

<正>People'sRepublicofChinaisoneofthemostrapidlydevelopingcountriesintheworldtoday.Thereisagreatdemandonhighlyactualandaccuratespatialinformationofthewholecountry,especiallyofWestChinawhichbecomesthefocusofdevelopmentoftheChinesegovernmentrightnowandinthenextyears,butwherestillnotenoughtopographicmapsareavailable.ThisraisesgreatchallengestothesurveyingandmappingcommunityinChina.FacingthenewchallengestheChineseAcademyofSurveyingandMapping(CASM)starteditspioneerworkearly2002toexplorenewtechniquesandtechnologiesavailabletodaytowardincreasingthemapproductivity.WithimportofaCCNS/AEROcontrolsysteminNovember2002,thefirstDGPS/IMU-basedphotogrammetricprojectinChinawassuccessfullyaccomplishedjointlybyCASM,theGermany-basedcompaniesIGIandTechedge.Twophotogrammetricblocksof1:4,000and1:20,000photoscales,respectively,wereflowninAnyang,China.Directgeoreferencingandintegratedsensororientationwereconducted.Resultsachievedwereprovenbyusinggroundcheckpointsandcomparedwiththoseofaerialtriangulation.Orthophotosgeneratedbasedondir     

Gold mineralisation and alteration of Penakacherla schist belt, India, constraints on Archaean subduction and fluid processes

In the Dharwar Craton, southern India, gold deposits are found mostly along the six arcuate shear zones passing through late Archaean greenstone belts (2.7 Ga). One such shear zone complex extends for about 400 km within and along the Ramagiri–Hungund schist belt. The Penakacherla sector of this shear zone is excellently exposed, enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration.Metamorphism and deformation under NE–SW compression associated with Archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists. Continued compression generated a 50–100-m-wide shear zone complex consisting of mafic phyllonites. Advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified, K-metasomatic assemblage mainly consisting of chlorite, amphibole, K-mica, plagioclase, ankerite, quartz, Fe-oxides, pyrite, chalcopyrite and arsenopyrite. Networks of quartz and carbonate veinlets, a few millimeters to a few centimeters thick, formed along the foliation planes giving rise to microscopic alteration envelope, in which individual veinlet systems are merged into one another to form a composite alteration system. Gold is found within these quartz veinlets, mafic phyllonites and at their mutual contacts.Hydrothermal fluids have modified the primary major, minor, trace and LREE compositions of host rocks such that their mutual behaviour became non-systematic. Some HFSE and HREE also show minor mobility but the overall REE pattern generally resembles that of the precursor mafic volcanic rocks. Mass and volume loss/gain by Si and Ca has made significant impact on Al, Ti and Zr abundances, which are generally immobile during hydrothermal alteration. However, element pairs such as Zr–Hf, V–Sc and Nb–Ta maintain primary inter-element ratios, although their absolute abundances are drastically diluted. Similarly, ΣREE in highly silicified and carbonatised samples are reduced, but patterns remain similar to those of relatively least altered mafic phyllonites with (La_N/Yb)_N between 1 and 3. In some samples, LREE enrichment is observed elevating in (La_N/Yb)_N from 3 to 11. Pathfinder elements and base metals such as As, Cd, Cu, Pb, Zn and Sb have been added along with the Au and Ag.δ¹³C of carbon varies from −16‰ to −21‰ suggesting a biogenic origin, whereas coexisting pyrite δ³⁴S ranges from 1‰ to 3‰, pointing towards the involvement of magmatic or average crustal sulphur. Overall concentrations of K, Rb, Sr, Ba, Nb, Ta, Ti, Cs, Cr, Co, V, Y and Sc and many of the ratios such as K/Rb, La/Sc, La/Yb indicate that metamorphism, devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks. Fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity.     

Geology and Hydrothermal Alteration of the Low Sulfidation

Abstract. The Pantingan Gold System (PGS) is a vein-type epithermal prospect exposed within the summit caldera of Mount Mariveles, Bagac, Bataan (Luzon), Philippines. It consists of nine major veins, eight of which trend NW-WNW and distributed in an en echelon array. The eastern tips of these veins appear to terminate near the NE-NNE trending Vein 1, which is located in the easternmost portion of the prospect. Metal assay results on vein and wall rock samples indicate concentrations of 0.01 to 1.1 g/ton Au, trace to 34 g/ton Ag and 0.003 to 0.02 % Cu. Andesite lava flow deposits host the PGS. Potassium-Argon isotopic dating of these andesites yields anarrow age range of 0.88± 0.13 to 1.13 ± 0.17 Ma. The surface exposures of the veins (up to 5 m wide) are encountered at different levels between 590–740 masl. These commonly display a massive texture although banding prominently occurs in Vein 1. The veins consist of gray to cream-colored crystalline and chalcedonic quartz and amorphous silica. Pyrite is the most ubiquitous sulfide mineral. It occurs either as fine-grained disseminations and aggregates in quartz or as infillings in vugs. Calcite, marcasite and bornite are also occasionally noted in the deposit. The prospect shows silicic, argillic, propylitic and advanced argillic alteration zones. Silicic and argillic alterations are confined in the immediate wall rocks of the quartz veins. Argillic alteration grades to a propylitic zone farther away from the veins. The advanced argillic alteration zone, indicated by a suite of acidic clay minerals that include kaolin-ite, dickite, pyrophyllite and alunite, might have been imprinted during the late stages of gold deposition. As a whole, the PGS displays geological and mineralogical features typical of gold mineralization in a low sulfidation, epithermal environment. It is also representative of a young, tectonically undisturbed gold deposit.     

招远黄埠岭金矿断裂构造性质及其控岩控矿作用

黄埠岭金矿主矿体产于灵北断裂带主断裂上盘次级断裂中,根据7号和10号矿体旁侧小角度斜交剪节理与矿体锐夹角指向的判断,控矿断裂具左旋性质。根据7号矿体旁侧节理统计及共轭剪节理产状的分析,黄埠岭矿区含矿断裂形成的最大主压应力方向为30°∠37°。NE向次级断裂是成矿前煌斑岩脉侵位的重要空间,也是主要的容矿构造。灵北主断裂带则主要扮演了一种导矿构造的作用。     

Synvolcanic gold mineralization within a deformation zone: the Chevrier deposit, Chibougamau, Abitibi Subprovince, Canada

The Chevrier gold deposit is located in the northeastern part of the Abitibi Subprovince within the Chevrier volcanic centre (CVC). This calc-alkaline volcanic centre evolved from mafic to felsic in a submarine environment, and the Chevrier deposit is spatially associated with the uppermost unit composed mostly of massive dacite to rhyolite, dated at 2730 Ma. The Chevrier deposit is divided in two zones. The North Zone is composed of high-grade, discordant quartz-carbonate veins and disseminated pyrite mostly within melanocratic gabbro dykes, whereas, the South Zone is within a low-grade, concordant pyrite envelope associated with quartz-carbonate-pyrite veinlets. Both zones are highly deformed and show strong carbonate, sericite and chlorite alterations. Although these zones share many characteristics with orogenic deposits, the crosscutting of the Chevrier deposit by structures associated with the major deformation events suggests that mineralization was prior to these events. Furthermore, felsic dykes associated with the formation of the CVC crosscut auriferous veins and zones, therefore suggesting a synvolcanic timing for the gold mineralization. Characteristics of the zones, such as similar vein composition and alteration mineral assemblages and location within the volcanic pile, suggest that they are part of a single hydrothermal event where the South Zone represents the shallower part of the deposit. The Chevrier deposit is classified as a noncarbonate-hosted stockwork and disseminated deposit and shows many similarities with strata-bound gold deposits of the Andacollo mining district of Chile. Dating of mineralization at the Chevrier deposit indicates that the emplacement of gold occurred more than 25 Ma before the onset of the orogeny affecting this part of the Abitibi subprovince. It also illustrates how synvolcanic mineralization can be misinterpreted as an orogenic deposit without the presence of crosscutting relationships with dykes, faults or other structures.Contribution No. 2005-5130-01 of the Ministère des Ressources naturelles et de la Faune du Québec.     

Gaseous transport and deposition of gold in magmatic fluid: evidence from the active Kudryavy volcano, Kurile Islands

The distribution of gold in high-temperature fumarole gases of the Kudryavy volcano (Kurile Islands) was measured for gas, gas condensate, natural fumarolic sublimates, and precipitates in silica tubes from vents with outlet temperatures ranging from 380 to 870°C. Gold abundance in condensates ranges from 0.3 to 2.4 ppb, which is significantly lower than the abundances of transition metals. Gold contents in zoned precipitates from silica tubes increase gradually with a decrease in temperature to a maximum of 8 ppm in the oxychloride zone at a temperature of approximately 300°C. Total Au content in moderate-temperature sulfide and oxychloride zones is mainly a result of Au inclusions in the abundant Fe–Cu and Zn sulfide minerals as determined by instrumental neutron activation analysis. Most Au occurs as a Cu–Au–Ag triple alloy. Single grains of native gold and binary Au–Ag alloys were also identified among sublimates, but aggregates and crystals of Cu–Au–Ag alloy were found in all fumarolic fields, both in silica tube precipitates and in natural fumarolic crusts. Although the Au triple alloy is homogeneous on the scale of microns and has a composition close to (Cu,Ni,Zn)₃(Au,Ag)₂, transmission electron microscopy (TEM) shows that these alloy solid solutions consist of monocrystal domains of Au–Ag, Au–Cu, and possibly Cu₂O. Gold occurs in oxide assemblages due to the decomposition of its halogenide complexes under high-temperature conditions (650–870°C). In lower temperature zones (<650°C), Au behavior is related to sulfur compounds whose evolution is strongly controlled by redox state. Other minerals that formed from gas transport and precipitation at Kudryavy volcano include garnet, aegirine, diopside, magnetite, anhydrite, molybdenite, multivalent molybdenum oxides (molybdite, tugarinovite, and ilsemannite), powellite, scheelite, wolframite, Na–K chlorides, pyrrhotite, wurtzite, greenockite, pyrite, galena, cubanite, rare native metals (including Fe, Cr, Mo, Sn, Ag, and Al), Cu–Zn–Fe–In sulfides, In-bearing Pb–Bi sulfosalts, cannizzarite, rheniite, cadmoindite, and kudriavite. Although most of these minerals are fine-grained, they are strongly idiomorphic with textures such as gas channels and lamellar, banded, skeletal, and dendrite-like crystals, characteristic of precipitation from a gas phase. The identified textures and mineral assemblages at Kudryavy volcano can be used to interpret geochemical origins of both ancient and modern ore deposits, particularly gold-rich porphyry and related epithermal systems.     

Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil

The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW–SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO₂ (CH₄-N₂) and CO₂ (CH₄-N₂)-H₂O-NaCl inclusions that show highly variable phase ratios, CO₂ homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18–33mol% of CO₂, up to 4mol% of N₂, and less than 2mol% of CH₄ and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ¹⁸O_H2O and δD_H2O (310–335°C) values of +6.2 to +8.4‰ and −19 to −80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ¹³C) varies from −14.2 to −15.7‰ in carbonates; it is −17.6‰ in fluid inclusion CO₂ and −23.6‰ in graphite from the host rock. The δ³⁴S values of pyrite are −2.6 to −7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO₂ reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site of deposition and sulfur isotopes indicate some oxidation of the originally reduced fluid. The deposition of gold is interpreted to have occurred mainly in response to phase separation and fluid-rock interactions such as CO₂ removal and desulfidation reactions that provoked variations in the fluid pH and redox conditions.