查看更多>>摘要：The Zaglic Au deposit is located in a Late Oligocene magmatic arc within the Arasbaran Magmatic Belt of NW Iran, which formed during the subduction of Mesotethys oceanic crust. Country rocks comprise intermediate to mafic volcanic and volcanoclastics of andesitic to trachy-andesitic composition, and exhibit late granite plutonism. Host assemblages display medium- to high-K calc-alkaline affinities with fractionated REE profiles, including Nb and Ti depletion and Rb, Ba, Th, U enrichment, consistent with subducted terranes. Wall-rock alteration comprises multi-stage silicic, sericitic, argillic and/or propylitic domains, associated with (i) pre-, (ii) main-, and (iii) post-ore emplacement. Pyrite is the dominant sulfide with spatially associated chalcopyrite and bornite in quartz vein and veinlets, with free gold occurring as microscopic grains in quartz, or as inclusions in pyrite. Fluid inclusion analysis of pre- (quartz I), main- (quartz II) and post-ore stages (quartz III) identifies liquid-rich, multi-stage, and vapor-rich varieties with decreasing temperatures and salinities, with the following Th and NaCl wt% equivalent ranges: pre-mineralization: 230-382 degrees C and 6.1-8.2; main-ore: 179-311 degrees C and 0.35-3.22%; and post-ore: 150-195 degrees C and 2.2-2.9%. Stable isotope analysis identifies variable delta 18Ofluid and delta Dfluid signatures, including: quartz I: 2-3.4%o; -86 to -78%o; quartz II: - 0.6-0.2%o; -89 to -85%o; sericite: -0.2 to 3.4%o; -107 to -91%o; and chlorite: -0.6 to 1.4%o; -115 to -104%o. Such ranges imply a mixture of magmatic and meteoric fluids, characteristic of a wide range of epithermal Au deposits. Sulfur isotope composition (delta 34S) of this deposit's two principal sulfide minerals is consistent with compositionally reduced mineralizing fluids including: pyrite: -1.4 to 2.7%o and chalcopyrite: -2.6 to 1.8%o. Geochronological analysis records 40Ar/39Ar dating of biotite from andesite porphyry with a plateau Eocene age of 48.20 +/- 0.73 Ma, together with ~8 Ma or Late Miocene ages from fine-grained sericite.
Lima, Ana T.Kirkelund, Gunvor M.Ntuli, FreemanOttosen, Lisbeth M....
13页
查看更多>>摘要：Metals, including rare earth elements (REE), are the cornerstone of our current and future low-carbon urban infrastructure. This study looks at different waste resources and contaminated materials present in the urban setting as REE sources. Wastes and other dilute sources such as incineration ashes, sediments, and mine tailings are not only essential sources of REE in achieving a circular, carbon-neutral economy but may be the most realistic one. E-waste, being the most REE concentrated waste, faces serious reservations regarding handling in large-scale facilities, and this waste is generally landfilled. In this study, we analyzed REE total concentrations and pH desorption curves in ten dilute sources of REE: Ferrochrome slag from a mine in South Africa, sediments retrieved form stormwater ponds in Denmark, coal fly ashes, municipal solid waste (MSW) fly ashes, wood fly and bottom ashes and sewage sludge fly ashes (ashes from different sources). After analyzing different residues, we found that coal fly ashes and stormwater retention pond sediments present the most promising ones. While coal fly ashes have the highest critical REE contents from the studied wastes, the sediments collected from a stormwater retention pond showed the highest REE leachability. We can find Nd, Dy, and Er - all critical REE - in sediments/soils near highways, coal ashes, and bauxite residue. Overall, coal fly ashes contain the highest critical REE contents found in the studied wastes but sediments collected from stormwater water ponds present the highest leachable REE. In fact, up to 100% of total REE found in these sediments are leachable at room temperature and low pH. Future REE resource extraction efforts should account for REE speciation in wastes and not only total contents.
Mees, FloriasMpinda, Martin T.Mujinya, Basile B.Kasangij, Patrick K....
8页
查看更多>>摘要：Using termite mounds as sampling medium for geochemical exploration is based on the assumption that mound construction results in upward transfer of particles that could reflect the composition of the underlying material. For large mounds such as those constructed by Macrotermes species, this is complicated by their dimensions and age. To investigate whether and how such mounds can be sampled to provide information about the nature of subsurface deposits, two Macrotermes falciger mounds built over mineralized deposits were sampled. For comparison, the soils around those mounds, as well as four control mounds in areas without mineralized deposits, were also sampled. Copper and cobalt concentrations were measured using hand-held XRF spectrometry, and chemical speciation analyses were performed for selected samples. The termite mounds built on mineralized deposits contained up to 9 times more Cu than the surrounding soils and up to 13 times more than termite mounds built over non-mineralized deposits. Cobalt concentrations were well above the detection limit in mounds on mineralized deposits, with values of up to 630 ppm, in contrast to the surrounding soils and the control mounds. Copper concentrations were found to be highest in the central basal part of the metal-bearing active mound. The speciation study showed that Co was predominantly in reducible form, whereas Cu was predominantly in both reducible and residual forms. Sampling of large termite mounds is confirmed as a possible tool in Cu-Co prospection, whereby it must be taken into account that metal distribution within the mounds is neither uniform nor static.
查看更多>>摘要：Detection of mineral system footprints in regions under thick cover is challenging. The difficulties are enhanced in regions with low-relief landscapes that are deeply weathered. This research examines how information from a single drill hole in an underexplored region can deliver a significant amount of information to assist in greenfields exploration. This study describes the geochemical dispersion processes through >500 m of cover based on observations from drill hole CDP008, and explores the possibility of recognising landscape features that link basement features with the surface.Our study revealed that: (1) the lower fluvial sandstone package contains a geochemical footprint of the underlying basement rocks, produced by vertical and lateral geochemical dispersion; whereas (2) the overlying sediments do not record any footprint of the basement rocks; and (3) the top limestone units are a chemical barrier for vertical geochemical dispersion due to their lack of permeability.Basement features identified from magnetic data are mimicked by linear surface landscape features that lie above them, which may potentially be associated with vertical geochemical dispersion processes, linking the basement with the surface. Hence from the point of view of mineral exploration, surface geochemical sampling should target these particular neotectonic/reactivation-associated features of the landscape.We suggest that in areas of deep cover, neotectonics/reactivation surface landscape features have the highest prospectivity to detect deep basement geochemical signatures at surface. The findings from this study may therefore impact approaches to mineral exploration under cover in similar landscape contexts around the world, such as regions in West Africa, India, China and Brazil.
查看更多>>摘要：Establishing the natural background levels of chemical elements is very often extremely complicated. This is even more true especially for the more anthropized areas, where the concentration of an element in the environmental matrices is conditioned not only by the natural (geogenic) context but also by anthropic activities. In this study, the natural background levels (NBLs) of several chemical elements in the stream sediments of the High Agri River basin have been calculated using a combination of multivariate statistical analysis (MSA) and machine learning techniques in the frame of compositional data analysis (CoDA). Specifically, data clustering and robust principal component analysis (rPCA) have allowed us to recognize and isolate three different data populations, belonging to three different geological domains. A first population of data is clearly related to calcareous lithologies, while the second one is associated to siliciclastic lithologies. A third one is of mixed origin, partly linked to the volcanoclastic nature of the sediments and due to the presence of co-precipitation phenomena. The three data populations have been later separated into three different databases and, whereas needed, the outliers have been eliminated. Based on the obtained results, the NBLs have been calculated using the US-EPA's (United States Environmental Protection Agency) ProUCL software. The results derived from this new approach have been later compared with those obtained using the spectral analysis (S-A) method to evaluate its advantages and versatility. This approach allowed calculating more reliable natural background values.
查看更多>>摘要：Surface soil sampling has been proved to be an effective and low-cost mineral exploration method in covered terrains. The critical question is to determine whether the surface anomalies originated from the mineralization at depth. Mercury isotope signatures have recently been employed as a tool for understanding the sources of Hg anomalies. Meanwhile, Hg is a traditional pathfinder for Au exploration. Can Hg isotopes be applied to trace the sources of Au anomalies in topsoils in covered areas? This is the first study that employed Hg isotopes as an exploration proxy for Au mineralization at depth. Surface soil samples over the concealed Shuiyindong Au deposit, China, were collected and their total Au (TAu), total Hg (THg) contents, and Hg isotope compositions were analyzed. Gold and Hg surface positive anomalies display high correlation indexes along the sampled traverse above the Shuiyindong Au deposit. Moreover, the Hg anomaly is significantly stronger than that of Au. Soils from deep ores-related areas show clearly positive 8202Hg values (-0.78%o to - 0.23%o, averaging -0.46 +/- 0.19%o, n = 10, 1SD) compared with those from the background areas (-1.67%o to -0.66%o, averaging -1.07 +/- 0.28%o, n = 10, 1SD). 8202Hg and 1/THg in deep ores-related soils have been altered by the ascending geogas from the mineralized rocks of the Longtan Fm. Soil positive Au anomalies detected in the study area are sourced at depth in the Shuiyindong Au deposit. However, it is not feasible to apply A199Hg to trace the anomalous Au sources in topsoils, because Hg(II) photoreduction can imprint the A199Hg signature, leading to negative A199Hg values in the soils. Semi-volatile Hg and ultra-fine Au particles are mobile and could continuously migrate from the depth to the surface through macro-structures and micro-fractures with the ascending geogas, then most of them are absorbed by the surface soils. Overall, this study successfully traced the Au deposit at >650 m depth using delta 202Hg, which is significant for mineral exploration of deep-seated Au deposits, especially in unknown covered areas.
查看更多>>摘要：The Sanjiang base metal metallogenic belt (SMB) in southwestern China is characteristic of composite mineralization during the India-Asia continental collision. However, the geodynamic settings of the composite processes of this belt are poorly understood. The Lanuoma deposit, located in the Changdu Basin in the central segment of the SMB, is a Zn-Pb-Sb polymetallic deposit. The cross-cutting relationships and paragenetic mineral associations suggest the superimposition of a late Sb-Pb mineralization event over an early Zn-dominant mineralization event. Calcite is the main gangue mineral, intergrown with late Sb-Pb minerals (e.g., boulangerite, zinkenite, sorbyite and plagionite). In situ U-Pb dating by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) was successfully carried out on calcite from this deposit, and restricts the Sb-Pb mineralization to 19.7 +/- 1.6 Ma, with a mean square weighted deviation (MSWD) of 1.2. This age is approximately synchronous with that of strike-slip shearing-related leucogranites in the marginal orogens; together with previous data, this result suggests that the contemporaneous magmatism significantly contributed to the ore forming fluids associated with the Sb-Pb mineralization. Overprinting of the Miocene Sb-Pb event in a trans tensional regime on the Oligocene transpression-driven Zn mineralization resulted in the characteristic Zn-Pb-Sb assemblage at Lanuoma. Moreover, this study indicates that the SMB holds great exploration potential for Sb(-Pb) resources.
查看更多>>摘要：The McKenzie Gulch (MG) copper-silver skarn occurrences are associated with the Middle Devonian intermediate to felsic dyke swarms. Mineralization occurs as veins and stockwork of veinlets, disseminations, patchy, and locally as replacement of calc-silicate skarns in argillaceous limestone. This skarn is interpreted to have developed in three stages: the earliest contact metamorphic stage resulting in hornfels developed from calcareous mudstone and very fine-grained clastic sedimentary rocks (Stage I); this was followed by metasomatic replacement resulting in prograde anhydrous skarn containing grossular-andradite (grandite), diopsidic pyroxene, and wollastonite (Stage II); increasing fluid/rock interaction results in retrograde skarn dominated by epidote, calcite, green amphibole, chlorite, sulfide minerals, titanite, andradite and hedenbergite commonly along veins and veinlets (Stage III). Subordinate sphalerite and pyrite occur in late veins cross-cutting both porphyry dykes, skarns and hornfels zone. Prograde garnets in the study area belong to the grossular-andradite solid solution that ranges from Adr(16)Gr(82) to almost pure andradite Adr(99)Gr(1), whereas other garnet end-members constitute less than 5% collectively. Pyroxenes form a diopside-hedenbergite solid solution with composition between Di(31)Hd(60) and Di(93)Hd(7), while other pyroxenes constitute less than 10% collectively. These garnets and pyroxenes exhibit chemical zonation patterns generally characterized by a rim of Fe enrichment relative to cores of grains, which may suggest possible change in salinity (or other factor that promotes Fe transport). This means grossular and diopsidic cores are rimmed by more andradite and hedenbergitic compositions for garnet and pyroxene, respectively. In general, there is a tendency for increasing Fe component in both garnet and pyroxene from the prograde to retrograde stages. Epidote formed during the retrograde stage exhibits oscillatory zoning similar to retrograde andradite and indicates Fe enrichment increasing from core to rim. Based on the major element composition, textural and optical characteristics of garnets, we conclude that grandites (Al-rich) formed under low water/rock ratios, in equilibrium with metasomatic fluids whose composition was locally buffered by the host rocks, whereas andradite (Fe-rich) resulted from relatively high water/rock ratios that were in equilibrium with a magmatic derived fluid. The results of this study indicate that there is a relationship between the composition of pyroxenes and garnets of the skarn alteration facies and the dominant metal of the mineralized skarns. These facies plot in the compositional field of Cu-dominated skarns. As a result, this relationship may be applied in exploration for skarn and porphyry copper mineralization.
NSTL
Elsevier