Arsenic mobility in mildly alkaline drainage from an orogenic lode gold deposit,Bralorne mine,British Columbia

The historical (1932–1971) Bralorne mine produced over 87 million grams of Au from an archetypal orogenic lode gold deposit in southwest British Columbia. High concentrations of As in mine drainage, however, represent an on-going environmental concern prompting a detailed study of effluent chemistry. The discharge rate at the mine portal was monitored continuously over a fourteen-month period during which effluent samples were collected on a quasi-weekly basis. Water samples were also collected on synoptic surveys of the adit between the portal and the main source of flow in the flooded workings. Total concentrations of As in the mildly alkaline (pH = 8.7) portal drainage average 3034 μg/L whereas at the source they average 5898 μg/L. As emergent waters from the flooded workings flow toward the portal, their dissolved oxygen content and pH increase from 0 to 10 mg/L and from 7.7 to 9, respectively. Near the emergence point, dissolved Fe precipitates rapidly, sorbing both As(III) and As(V). With increasing distance from the emergence point, dissolved As(III) concentrations drop to detection limits through sorption on hydrous ferric oxide and through oxidation to As(V). Concentrations of dissolved As(V), on the other hand, increase and stabilize, reflecting lower sorption at higher pH and the lack of available sorbent. Nonetheless, based on synoptic surveys, approximately 35% of the source As load is sequestered in the adit resulting in As sediment concentrations averaging 8.5 wt%. The remaining average As load of 1.34 kg/d is discharged from the portal. Partitioning of As(V) between dissolved and particulate phases in portal effluent is characterized by a sorption density of 0.37 mol As (mol Fe)⁻¹ and by a distribution coefficient (K_d) of 130 L/g HFO. The relatively high sorption density may reflect co-precipitation of As with Fe oxyhydroxides rather than a purely adsorption-controlled process. Results of this study show that the As self-mitigating capacity of drainage from orogenic lode gold deposits may be poor in high-pH and Fe-limited settings.     

Geochemistry of coals from the Elk Valley coalfield, British Columbia, Canada

The Elk Valley coalfield of British Columbia is one of the major coal producing areas in Canada. The coals are of Cretaceous and Jurassic–Cretaceous age and range in rank from high-volatile to low-volatile bituminous (%Ro_max: 0.8–1.6). Coal seams from outcrops and active mines in this coalfield were analysed for rank and maceral composition using reflected light microscopy, for geochemistry using AAS, INAA, and ICPES, and also by proximate and ultimate analyses. The Elk Valley coal seams contain low average concentrations of hazardous elements such as As, Mo, Pb, and Se. However, there are seams that contain relatively high concentrations of some of these elements, such as 8 mg/kg and 108 mg/kg of arsenic. When the geochemistry of coal seams is compared within the different parts of the coalfield, the elemental composition amongst the seams from various sections located in the central area of the coalfield is similar. Coal seams in the northern area of the coalfield have different geochemistry than coal seams in other areas of the coalfield; seams in the northern area have much higher As, Br, Cr, Cu, Fe, K, and Na content, but contain less Ca.     

加拿大Abitibi 绿岩带Donalda金矿近水平含金石英脉的显微构造分析及其对成矿流体动力学的指示

位于加拿大Abitibi 绿岩带南部的Donalda 金矿床主要由近水平的、与剪切带近垂直的含金石英脉组成,矿脉厚度0.3~0.5 m,含大量与脉壁平行的条带,指示多期次裂隙扩张和矿物沉淀。原生石英 c轴方位测量显示石英生长方向垂直于脉壁,指示断裂属张性,矿物沉淀属空间充填。显微裂隙、细脉及流体包裹体面 (FIPs) 的方位测量指示原生矿物受到了近直立的最大主压应力(σ1) 作用,与区域性的、近水平的南北向挤压应力不符。这一矛盾现象可用流体压力在超静岩和静水压力之间周期性变化及近水平断裂的周期性张开与闭合来解释。当流体压力大于静岩压力时,断裂张开,原生矿物沉淀,而当流体压力减小时,断裂上盘往下垮,两盘突出的矿物碰撞、碾压形成与脉壁平行的变形条带。由于断裂两盘岩石不是沿整条断裂都互相接触,两盘相顶部分承受的垂直应力大于水平方向的挤压应力, 这就解释了为什么显微构造指示近直立的最大主压应力(σ1)。这个流体构造模式支持断层阀模式,并且无须改变区域应力场就可解释脉体内局部主压应力的变化。     

Geostatistical investigation of the Kutcho Creek chrysotile deposit,Northern British Columbia

The Kutcho Creek asbestos deposit, owned by Cassiar Asbestos Corporation Ltd., has been sampled by two major exploratory programs that have provided two sets of grade data—one from the horizontal direction (wall readings) and one from the vertical direction (diamond drill cores). These data (percentage chrysotile by volume) were divided into well-defined groups on the basis of location and sample continuity, and experimental variograms for percentage of fiber content were calculated for each group. Horizontal data were all oriented in directions roughly parallel to the trend of an elongate serpentinite zone containing local centers rich in chrysotile veinlets. Spherical variogram models fitted to horizontal and vertical data sets are as follows: Vertical: $$\begin{gathered} \gamma (h) = 0.27 m^2 + 0.44 m^2 [(3h/70) - (h^3 /85,750)] h \leqslant a \hfill \\ \gamma (h) = 0.71 m^2 h \geqslant a \hfill \\ \end{gathered}$$ Horizontal: $$\begin{gathered} \gamma (h) = 0.27 m^2 + 1.20 m^2 [(h/60) - (h^3 /729,000)] h \leqslant a \hfill \\ \gamma (h) = 1.47 m^2 h \geqslant a \hfill \\ \end{gathered}$$ Wherem is the mean value of data used in the construction of a variogram,h is a lag (sample spacing), anda is the range over which the grade is autocorrelated. These two one-dimensional models can be combined to a two-dimensional model with the form γ(h)=γ(r)+γ(x) where γ(r) is an isotropic component (equivalent to the vertical model above) and γ(x) is a zonal component in the horizontal direction (equivalent to the difference between the horizontal and vertical models above). This general model describes data throughout the entire serpentinite zone in a satisfactory manner but, of course, does not contain information in the third dimension, and, thus, cannot be used as a basis for grade and tonnage calculations and corresponding error estimates. Nevertheless, the analysis has illustrated the potential of variogram analysis for such tonnage and grade calculations. Furthermore, the study has provided limiting two-dimensional information on the geometry of chrysotile-rich zones within the serpentinite belt, information that can be used to advantage in planning future exploratory drilling.     

Geochemistry of iron ochres and mine waters from Levant Mine,Cornwall

The geochemistry of metal-rich mine waters and mineral precipitates from the Levant mine, Cornwall, has been examined. Sulphide oxidation at Levant mine has produced a wide range of secondary sulphides, oxides, chlorides, sulphates and carbonates in a gossan environment. The mine waters display a wide variation in alkalinity, pH, chloride, sulphate, sodium, potassium and heavy metal content which can be explained by variable degrees of mixing between acidic, metal-rich, rock drainage waters and neutral to alkaline sea waters. Transition metals are soluble in the acidic mine waters with concentrations up to 665 mg/l Cu, 41 mg/l Zn, 76 mg/l Mn, 6 mg/l Co and >2500 mg/l total Fe. The production of acid rock drainage and leaching of metals can be related to sulphide oxidation. Where these metal-rich acidic waters mix with infiltrated sea water, neutralization occurs and some metals are precipitated (principally Cu). Where pools of mine drainage are stagnant native copper and cuprite are precipitated, frequently observed replacing iron pipes and rail tracks and wooden shaft supports, due to electrode potential differences. In these solutions, dissolved copper species are also reduced by interaction with wood-derived organic species. Precipitation of iron oxyhydroxides, caused by a pH increase, also occurs and leads. to coprecipitation of other metals, including Cd, Co, Ph, Mn, Ag and Zn, thus limiting the release of dissolved metals in solution from the mine. However, the release of suspended metal-rich ochres in mine discharge waters (with high Ph, Zn, Cd, Mn, Ni, Sn, Sb, As, Bi, Cu, Co and Ag) will still present a potential environmental hazard.     

Organic petrology of Hat Creek coal deposit No. 1, British Columbia

Gell preserved monocotyledon and peeridophyta remains were found in natural bitumen frrm Iranian, tar pit and oil seeps, using reflected and fluorescence light microscopy. The plant tissue are impregnated or partially replaced by bitumens the extent of this replacement is noted.     

Geochemistry of the mineral waters and gases of the Mukhen deposit,Far East

This work reports new hydrochemical data on the two types of cold high p CO₂ groundwaters from the Mukhen deposit (Khabarovsk district). The first type is classed with HCO₃-Ca-Mg waters with a relatively low TDS (up to 1.7 g/l) and high concentrations of Fe²⁺, Mn²⁺, Ba²⁺, and SiO₂. The second type is of HCO₃-Na composition with high TDS (up to 14 g/l) and elevated Li⁺, B, Sr²⁺, Br^?, and I^?. New oxygen (δ¹⁸O) and hydrogen (δD) isotopic data on the waters and carbon (δ¹³C) isotopic data on the gas phase, together with a detailed geological and hydrogeological analysis of the study area, allowed us to decipher the origin of both the mineral waters. Based on the tritium content (³H) in the ground and surface waters of the area, the duration of the mineral water circulation was estimated. It was established that the both types of groundwaters were formed during interaction of meteoric water with bedrock under active influence of CO₂, however HCO₃-Na groundwaters have longer residence time than HCO₃-Ca-Mg groundwaters.     

Fluid source and thermal history of an epithermal vein deposit,Owen Lake,central British Columbia: evidence from bitumen and fluid inclusions

Fluid source and thermal history are determined for the barite and bitumen-bearing, early Eocene (ca. 50 Ma) polymetallic, epithermal veins of the Owen Lake deposit, central British Columbia, Canada. Carbon isotopic values for the bitumen are highly negative (δ ¹³ C ca −29%) indicating a probable terrigenous source, which may be 1 no older than Late Cretaceous or, 2 Eocene plant-fossil-bearing units stratigraphically above the Owen Lake deposit. Heat generated by suspected magmatic activity resulted in downflow of meteoric water and upflow of hydrothermal water, mixing at the site of deposition. Aqueous and hydrocarbon fluid inclusions occur within barite; Th of both types of inclusions indicate a temperature range of approximately 100° to 180 °C. Tm(ice) of aqueous inclusions range from −4.5 to −0.2 °C indicating a range of 7.2 to 0.4 equivalent weight percent NaCl. Parageneticaly younger bitumen has a vitrinite reflectance of 0.6% indicating maturation level in the temperature range of 80° to 120 °C, strongly suggesting a cooling thermal regime during barite and bitumen deposition, consistent with a late stage paragenesis.     

Uranium depositional controls at the Prairie Flats surficial uranium deposit, Summerland, British Columbia

A hydrological and geochemical investigation of the Prairie Flats surficial uranium deposit in Summerland, BC was undertaken to identify the principal controls on uranium deposition. A network of piezometers was installed and used to measure the hydraulic conductivities of the host sediments as well as the general flow direction and aqueous geochemistry of the resident groundwaters. Two hydrostratigraphic units were identified: a peat and clay unit overlying a sand and gravel unit. Measured hydraulic conductivities were on the order of 10^-7 and 10^-5 m/s, respectively, and the vertical hydraulic gradients indicate significant groundwater discharge upward into the peat and clay unit. Prairie Flats groundwaters are neutral to alkaline in pH, enriched in Ca²⁺ and HCO₃^-, and have dissolved uranium concentrations ranging from 10 to nearly 1,000 µg/l. Groundwater flow and geochemistry data were used to estimate the flux of uranium in groundwater at the site. A major fraction of the uranium is taken up by adsorption to organics. There is also evidence for subsequent desorption by the formation of soluble complexes with bicarbonate. Uranium that is not held by adsorption is most likely precipitated as uraninite, UO_2(c). Reducing conditions in the peat and clay unit (Eh<0.1 V) relative to the underlying sand and gravel unit (Eh>0.2 V) may explain the high concentrations of uranium nearer ground surface. The current flux of uranium into the flats is significantly smaller than that calculated from the size and age of the deposit, which may be an indication of changing rates of deposition in response to varying climatic and hydrogeologic conditions over time.     

Lithogeochemistry of hypogene, supergene and leached cap samples, berg porphyry copper deposit, British Columbia

In this paper we examine the influence of the development of supergene oxide and sulphide zones on the original hypogene geochemical patterns at the Berg deposit, British Columbia.The deposit, in the alpine zone of the Tahtsa Range, was logged (GEOLOG) and sampled in fourteen diamond drill holes along a N—S section and from outcrop where possible. Anomalous populations of major and trace elements were defined using log probability graphs and a sequential extraction (10% hydrochloric acid— ammonium oxalate — potassium chlorate/hydrochloric acid — nitric/perchloric acids) was used to study the distribution of elements between carbonate, oxide, sulphide and silicate phases.Core logs and assays show that primary ore minerals (chalcopyrite—molybdenite) extend from the outer part of the porphyry intrusion into the surrounding hornfels where the best grades of copper are found close to the intrusive contact. Maximum copper grades, however, result from development of a supergene enrichment blanket. Within the hypogene zone, principal lithogeochemical patterns reflect the differences in composition of the hornfels, originally intermediate to basic volcanics, and the intrusion, as well as the introduction of F and trace metals (Cu, Mo, Pb, Zn and Ag). Distribution of Ag is broadly comparable to that of Cu and Mo whereas anomalous Pb and Zn are present as peripheral haloes around the potential ore zones.Emergence of strongly acidic ground water and precipitation of iron oxides, indicate that leaching processes are active. Furthermore, although primary sulphides, associated with both their oxidation products and secondary sulphides, can still be found in surface samples, sequential extractions on drill core clearly indicate vertical redistribution of copper between oxide, carbonate and sulphide phases. Using ratios of metal concentrations to TiO₂, the surface concentrations of trace metals can be compared with those at depth and the relative amount of enrichment or depletion can be quantified. In highly leached sites the absolute concentrations of Cu, Mn and Zn are low which is reflected in TiO₂ ratios of <1. However, Mo, Pb and Ag are enriched at the same sites (TiO₂ ratios >1). In areas where physical erosion exceeds leaching (topographic lows) primary sulphides co-exist with secondary sulphide and oxide minerals. Here Cu, Mo, Pb, Zn, Mn and Ag are enriched. Fluorine is relatively unaffected by the leaching process. It would appear signature for a cale alkaline Cu and Mo porphyry deposit in an area where outcrop was intensely leached.     

Compositional variation in Hg-bearing sphalerite from the polymetallic Eskay Creek deposit, British Columbia, Canada

The Eskay Creek, British Columbia, Canada, is a polymetallic, gold- and silver-rich, volcanic-hosted, massive sulfide deposit. The ore in the deposit is divided into subzones distinguished by mineralogy, texture, grade and metallurgical characteristics. This study presents the results of a mineralogical examination of three composite field samples, with emphasis on the chemistry of sphalerite. Sphalerite is associated with variable amounts of Hg-tetrahedrite and cinnabar, and an array of sulfides, sulphosalts and non-opaque minerals. Electron micro probe analyses of sphalerite in the three composite samples reveal wide variations in compositions. The Hg content in sphalerite in the three samples varies between 0.08 and 16.35 wt%, whereas the Fe content ranges from 0.33 to 2.29 wt%. The chemical formula of the sphalerite shows the compositional range (Zn_0.89–0.98Hg_0.01–0.09.Fe_0.005–0.02)S. Sphalerite exhibits an almost perfect substitution of Hg and Zn, as shown by the negative covariance between them. Sphalerite with the highest Hg contents tends to have the lowest Fe concentrations. The highest Hg contents in sphalerite are recorded in the samples with the highest bulk Hg concentrations and with the highest cinnabar contents.

The compositional variations of sphalerite are important because they can be used in mapping ore forming fluids and indicate possible temporal variations. Second, determination of the compositional variation of the sphalerite in the mine has metallurgical implications because the mineral is an important Zn source. The mineralogical data indicate that non-physical processes (e.g. pyrometallurgy) must be used to separate Hg from Zn concentrates, with direct environmental implications, that is, release of metals, such as Hg, into the environment during mining and processing.     

Mercury in subsurface and mine waters at Aktash ore deposit

In a weakly mineralized, weakly alkaline aqueous halo of mercury ores, Hg migrates mainly as a hydroxide and also as complexes from which it cannot be precipitated by H₂S. This latter form of “bound mercury” may broaden the halo and dissipate the metal over long distances.     

Carbonatization and propylitic alteration of fragmental basaltic rocks, Quesnel River gold deposit, Central British Columbia

The Quesnel River gold deposit (1.2 million tonnes grading 5.22 g/t Au in three separate zones) occurs within Takla Group volcanic rocks of Upper Triassic age proximal to an alkalic stock. The deposit occurs in amphibole-augite phyric, fragmental, basaltic rocks. Alteration has produced an assemblage of epidote-chloritetremolite-calcite-quartz with lesser pyrite, chalcopyrite, pyrrhotite, sphalerite, marcasite, galena, arsenopyrite and gold.The West Zone comprises a tabular, conformable sulfide body underlain by bedded, variably altered fragmental basaltic rocks and overlain by siltstone and argillite. In the Main Zone, highest gold grades occur adjacent to a sharp discordant alteration front with barren, strongly carbonatized, pyritic basaltic lapilli-tuff. It is overlain by siltstone and argillite and bounded to the east and a depth by a west dipping reverse fault. To the west the auriferous, propylitically altered, rocks grade laterally into lower grade and barren basaltic rocks.Oxygen(¹⁸O = + 9 to + 15) and carbon (¹³O= -14 to –7) isotopic signatures of calcite from carbonate-altered and propylitically altered rocks are similar. However, sulfur isotopic values for pyrite are different, with gold-associated pyrite (³⁴S = –7 to –3) distinct from pyrite in carbonate altered rocks with (³⁴S = + 8 to + 13).The carbonization occurred before complete induration of the basaltic fragmental rocks, whereas propylitization and gold plus sulfide precipitation is clearly epigenetic.     

Geochemistry of carbonated mineral waters from the Fadeevskoe deposit of the Primorye region

The geochemical study of bed rocks, underground and surface waters, and associated gases in the Fadeevskoe deposit of carbonated waters (Sikhote Alin, Primorye region) revealed that the chemical composition of these waters is formed in the zone of active water exchange in the limited area of the discharge zone, where hydro carbonate calcic waters with mineralization of up to 1 g/1 are formed in largely potassic-sodic rocks. Calculations of the saturation indices show that the mineral waters are characterized by the early stage of Ca saturation, being undersaturated with carbonates and aluminosilicates. The main factors that influence the water mineralization are the excess carbon dioxide in water and the circulation time. The oxygen and carbon isotope ratios indicate the atmospheric genesis of the aqueous component (δ²H = —117; δ¹⁸O = —15.4%o) and the carbon isotope content in the CO₂ implies the mantle nature of the carbon dioxide (δ¹³C = -9.9%o).     

海沟金矿区28号含金石英脉勘探历程

海沟金矿区28号含金石英脉由于它的形态、产状、品位等变化大、成矿后断裂破坏等原因,先后经历了5次勘探工作才基本上搞清了它的总体特征。本文通过介绍各阶段的勘探工作概况,总结勘探工作中存在的问题以及经验教训,指出勘探工作中的综合研究工作的重要性。     

Epithermal mineralization and ore controls of the Shasta Au-Ag deposit, Toodoggone District, British Columbia, Canada

The Shasta gold-silver deposit, British Columbia, Canada, is an adularia-sericite-type epithermal deposit in which deposition of precious metals coincided with the transition of quartz- to calcite-dominant gangue. Mineralization is associated with stockwork-breccia zones in potassically altered dacitic lapilli tuffs and flows, and consists of pyrite, sphalerite, chalcopyrite, galena, acanthite, electrum and native silver. Pre- and post-ore veins consist solely of quartz and calcite, respectively. Fluid inclusion microthermometry indicates that ore minerals were deposited between 280 ° and 225 °C, from a relatively dilute hydrothermal fluid (˜1.5 wt.% NaCl equivalent). Abundant vapor-rich inclusions in ore-stage calcite are consistent with boiling. Oxygen and hydrogen isotopic data (δ¹⁸O_fluid = −1.5 to −4.1‰; δD_fluid = −148 to −171‰) suggest that the fluid had a meteoric origin, but was ¹⁸O-enriched by interaction with volcanic wallrocks. Initial (˜280 °C) fluid pH and log f O₂ conditions are estimated at 5.3 to 6.0, and −32.5 to −33 bar, respectively; during ore deposition, the fluid became more alkaline and oxidizing. Ore deposition at Shasta is attributed to localization of meteoric hydrothermal fluids by extensional faults; mineralization was controlled by boiling in response to hydraulic brecciation. Calcite and base metal sulfides precipitated due to the increase in pH that accompanied boiling, and the associated decrease in H₂S concentration led to precipitation of gold and silver. Received: 23 February 1995 / Accepted: 16 April 1996