Quartz-sericite Schist Research Articles

The Lanseria palaeosol: Implications for palaeoweathering and terrestrial life at ∼2.6 Ga on the Kaapvaal Craton

Archaean palaeosols are a rare record of surface processes on the early Earth. We report on the discovery of a palaeoweathering profile developed at the contact between Mesoarchaean basement and the Neoarchaean to Palaeoproterozoic Transvaal Supergroup along the northern margin of the Johannesburg Dome, Kaapvaal Craton. Granodiorite ∼3.1 Ga old was subjected to weathering just prior to the deposition of the ∼2.6 Ga Black Reef Formation. The ∼25 m-thick profile is dominated by a palaeosaprolite and organic matter-rich palaeosol remnant at the top that experienced erosion upon marine transgression on the Kaapvaal Craton. The Al concentration of the profile, sericite content and chemical index of alteration (CIA) values progressively increase from the parent granodiorite towards the nonconformity as Fe, Mg, Na and Ca concentrations decrease. The decrease of Co and Zn together with Fe and the retention of U, V and Cr collectively suggest a reducing and acidic environment at the time of weathering. Carbonaceous matter with negative δ13C isotopic values (−27 to −23 ‰V-PDB) in the palaeosol is compatible with the former presence of photoautotrophic microbes. Copper depletion and mobility of P may indicate the presence of organic acids that enhanced chemical weathering of the bedrock. The palaeoweathering profile was subjected to diagenetic-hydrothermal K-metasomatism, regional metamorphism and deformation, which collectively transformed the regolith into a quartz-sericite schist, as it presently occurs. Despite these modifications, the original record of palaeoweathering and microbial colonisation is well preserved. Colonisation of a large swath of the Kaapvaal Craton by terrestrial soil-dwelling microbiota at 2.60 Ga is recorded in abundant soil-derived carbonaceous matter in transgressive marine conglomerates that erosively overlie the palaeosol.

Genesis of the Samba Cu deposit of the Central African Copperbelt in Zambia: Constraints from geochemistry and geochronology

The Samba Cu deposit is located in pre-Katangan Supergroup basement metavolcanic rocks of the Central African Copperbelt in Zambia. To better understand the formation of the Cu deposit, we use geochronologic, geochemical, and S isotopic data obtained for the deposit’s host rocks and sulfide minerals. Laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) dating of zircon from host rocks, including quartz-sericite schist and biotite-sericite-chlorite schist, yields ages of 1967 ± 17 Ma and 1960 ± 20 Ma, which are interpreted as the crystallization ages of the original volcanic rocks. Re-Os analyses of molybdenite intergrown with chalcopyrite constrain sulfide deposition to 548.1 ± 7.5 Ma and 524.1 ± 7.3 Ma, which correspond to the timing of the Cu mineralization. LA-ICP-MS U-Pb analyses of metamorphic rutile from the biotite-sericite-chlorite schist yield a U-Pb age of 508.3 ± 6.6 Ma, which is interpreted to represent the age of regional metamorphism. The new data suggest that the Cu mineralization at Samba was synchronous with the Lufilian orogeny.

Localization patterns of gold mineralization in the Phuoc Son area, Central Vietnam

Background. In this paper, the authors aim to reveal the localization patterns of gold mineralization in the Phuok Son region of Central Vietnam, which formed a Proterozoic-Cambrian metamorphic complex in the zone of the Late Paleozoic Benzhang–Queshon granite block.Aim. To determine the localization patterns of gold mineralization in the Phuoc Son area, Central Vietnam.Materials and methods. The research was based on geological materials, as well as mine working and appraisal well data. The material composition of the materials was studied using 15 transparent sections and 18 polished sections. In total, 127 samples were subjected to atomic absorption spectroscopy.Results. Within the Phuoс Son gold ore field in Central Vietnam, the site of the Baidat and Baigo mines located in the zone of reverse-shear termination was investigated. Here, the gold ore bodies are represented by quartz-sulfide veins subparallel to schistosity. The ore-bearing zones are layered zones of tectonic faults, which formed at the end of the reverse-shear period and complicated the western limbs and locks of the anticlines. These zones were formed under regional sublatitudinal horizontal stresses. The horizons of carbonaceous quartz-sericite schists are of great importance in ore control. There are steeply dipping post-ore faults that displace ore bodies. Two gold mineralization stages can be distinguished. The early stage was characterized by a wide development of sphalerite and a smaller amount of gold. The later stage was associated with the main precipitation of gold and formation of galena. According to the geochronological data on the argon isotopy in biotite, the gold mineralization at Baidat and Baigo was probably formed in the Triassic (250–200 Ma ago), at the stage of extinction of the regional metamorphism of the Indosinian orogenyConclusion. The results obtained should be used when conducting local forecasting of gold deposits in Central Vietnam.

Geology and pyrite-polymetallic mineralization of the forecasted
 Limonite deposit, Rassokhinsky ore cluster (Yenisei ridge)

The development of Russia’s largest Gorevskoye leadzinc
 deposit (Gorevsky GOK, Novoangarsky OK) will
 depend on promising deposits of the Angara polymetallic
 ore region, in particular, those of the Rassokhinsky
 ore cluster. Based on the analysis of geological and geophysical
 information of previous and current studies,
 a major Limonite pyrite-polymetallic (massive sulfide)
 deposit is forecasted within it. The main lithological
 and stratigraphic criterion for the localization of ores is
 determined by their confinement to high-carbon black
 quartz-sericite schists of the upper subformation of the
 Potoskuy suite of the Upper Riphean. In the top of this
 pack, layered and massive pyrite-polymetallic ores, 70–
 140 m thick, are localized. Based on PPA data, lead and
 zinc content in core varies from fractions of a percent
 to several percent, based on the ICP-AES method: 0,1–
 3,7 % Pb, 0,1–6,4 % Zn, Pb : Zn ratio is 1 : (1–10).

Comparative assessment of slope stability in weathered schists using Q-slope and LEM

The slope stability in weathered schists formations has always been of great importance for studies in rock mechanics. The majority of the methods used in the geotechnical practise for estimating the slope stability are based on the traditional limit equilibrium methods, analysing the possibilities of circular and non-circular failures. On the other side, very few empirical methods exist for assessment of the slope stability. Q-slope is a relatively new methodology for the assessment of slope stability in terrains built from rock masses. This method was developed over the last decade by Barton and Bar (2015, 2017), with modification of the original Q-system and it is based on the results of more than 500 case studies all over the world in reinforcement-free slopes. This paper presents results of the slope stability assessment with the limit equilibrium and Q-slope method at four characteristic cut sections with unusual general heights (ranging from 30 m to 92 m), along the route of the A2 motorway, section Kicevo-Ohrid in the Republic of N. Macedonia, which is under construction. The subject cuts presented in this paper were excavated in the period 2014 – 2018 without the application of special measures for protection. The research area is built mainly from phyllite, sericite schists, quartz-sericite schists and graphitic schists, which are folded, tectonically disturbed and affected by the process of degradation. According to the results of the analyses, it can be emphasised that both limit equilibrium method and Q-slope are applicable at terrains built from weathered and tectonically disturbed schists because the stability conditions on site were confirmed with these two methodologically different approaches. As a general conclusion, we can summarize that the best way to assess the slope stability condition is when we combine different tools and methodologies, especially when we face highly variable rock mass conditions.

Stability evaluation of cut slopes in highly weathered schists using limit equilibrium, kinematical and empirical methods

1. Extended abstractThe traditional limit equilibrium method and the kinematic analyses are the first choices in the geotechnical practice for the assessment of the slope stability of a particular rock slope. The reason is that very few empirical methods exist for this purpose.This paper presents results of the slope stability assessment with limit equilibrium, kinematical and empirical methods for over 50 deep cut slopes in highly weathered schists along the A2 motorway section Kicevo-Ohrid in RN Macedonia. The research area is mainly composed of phyllite, sericite schists, quartz-sericite schists and graphitic schists. These rocks are highly weathered, tectonically disturbed and often folded, which means they are prone to local deformations, especially in aspects of the long-term impact of atmospheric influences and the existence of unfavourable joint sets. Although most of the failures that occurred had local character, on several cut slopes global failure occurred. The slope stability assessment of the subject rock formations is a difficult challenge because the highly weathered phyllite and schists are difficult to be characterised, considering the uncertainties associated with the material anisotropy and the network of discontinuities.This study employs different failure mechanisms of cut slope stability in complex geological media. The rock masses were modelled according to the generalized Hoek-Brown criterion while the joints behaviour was modelled using the Barton-Bandis shear strength criterion. Rocscience software package was used for executing the limit equilibrium analyses and the stability analyses along discontinuities. The relatively new and intuitive empirical method Q-slope was applied for the stability assessment of the excavated rock slopes.According to the results and the findings, it can be emphasized that although the limit equilibrium analyses showed relatively stable slopes, significant failures on several cut slopes occurred on site. The stability conditions on site were confirmed with the kinematical analyses and the Q-slope method.The final decision of the slope geometry should be made after the inspection of the excavated surfaces because it is very difficult to register the discontinuity conditions before the construction phase starts. The best way to assess the stability condition is with a combination of different tools and methodologies, especially when we face highly weathered rock formations.The next step of this research will be to propose a methodology, where the long-term rock slope stability and the associated level of risk will be evaluated using graphical diagrams.

Study of Sericite Quartz Schist Coarse-Grained Soil by Large-Scale Triaxial Shear Tests

The large-scale triaxial consolidated-drained (CD) and consolidated-undrained (CU) shear tests were carried out to investigate performances of the sericite quartz schist coarse-grained soil on stress-strain, deformation, and strength under four different confining pressure conditions. The test results indicated that the stress-strain curve of sericite quartz schist was nonlinearity, compressive hardening and elastic-plastic. The shear strength envelope curve was better. In the triaxial CD shear test, the sericite quartz schist exhibited weak strain softening under different confining pressures. The sample showed shearing shrinkage at first and later dilatancy under confining pressures of 200, 400, and 600 kPa. When the confining pressure was 800 kPa, the sample showed a trend of shearing shrinkage. In the triaxial CU shear test, the sericite quartz schist exhibited strain hardening, presenting a tendency of shearing shrinkage at first and later dilatancy. It is more reasonable to take account of the cohesion of sericite quartz schist in practical engineering design by linear-regression analysis.

Genesis of the Baiyun pyrophyllite deposit in the central Taihang Mountain, China: Implications for gold mineralization in wall rocks

Genesis of pyrophyllite alteration can provide important clues for ore prospecting due to its various relationships with metallic mineralization. The Baiyun pyrophyllite deposit in the central Taihang Mountain (CTM) of the North China Craton (NCC) provides a natural case to gain insights into the genesis of pyrophyllite alteration and its relationships with gold mineralization in the wall rocks. The pyrophyllite ores primarily occur as subparallel-sheeted veins in fractures of the late Archean meta-volcanic rocks, and locally as filling fractures within the meta-intrusions. Phyllic alteration halos around the pyrophyllite orebody decline outwards, where gold mineralization develops as disseminated aggregates in honeycomb-like pyrites. Pyrophyllite ores are mostly dominated by 1TC-type pyrophyllite, sericite and quartz with minor kaolinite, illite and albite as identified by XRD analyses. Zircon grains from the granitic porphyry in the ore field define a weight mean U-Pb age of 130 ± 1 Ma (MSWD = 1.8, n = 19), and those from the sericite quartz schist yield an upper intercepted U-Pb age of 2551 ± 8 Ma. Zircon grains from the pyrophyllite ore yield an upper intercepted U-Pb age of 2566 ± 11 Ma and a lower intercepted age of 136 ± 7 Ma (MSWD = 0.99; n = 20), reflecting a Mesozoic magmatic-hydrothermal event, which could possibly be triggered by the lithospheric destruction of the NCC. LogƒO2-pH diagram suggests the fluids responsible for pyrophyllite alteration are extremely acidic (pH = 2.20) and under high oxygen fugacity (>ΔHM + 2.14). Calculated H-O isotopic compositions (δDH2O = −34 to −20‰; δOH2O = 3.4 to 7.5‰, 270 °C; δOH2O = 0.2‰ ~ 4.3‰, 200 °C) of pyrophyllite ores display typical features of volatile-dominated fluids with minor impact of meteoric water. Metal concentrations of pyrophyllite ores decrease with increasing contents of SiO2, suggesting the fluids generating pyrophyllite alteration are not conductive to gold mineralization. The results herein indicate that the Baiyun pyrophyllite deposit, formed as magma degassing in deep, are similar to the common root zones of advanced argillic lithocaps (barren shoulders) from porphyry environments and probably be the signs for erosion of epithermal deposits at shallow crustal depths.

The Tongkuangyu Cu Deposit, Trans-North China Orogen: A Metamorphosed Paleoproterozoic Porphyry Cu Deposit

AbstractThe Tongkuangyu copper deposit in the Zhongtiaoshan region, southern Trans-North China orogen, is hosted by a poorly constrained sequence of Paleoproterozoic volcano-sedimentary (quartz-sericite schist and biotite schist) and granitic rocks that have been metamorphosed to lower greenschist facies and variably deformed. The deposit has previously been proposed to be either a porphyry-type or a sediment-hosted stratiform Cu deposit, and its age of formation has been debated.The quartz-sericite schist is interpreted to be a felsic crystal tuff and consists of angular quartz crystals in a fine-grained sericite-altered matrix. Two quartz-sericite schist samples yielded zircon U-Pb upper concordia intercept ages of 2512 ± 12 (2σ, mean square of weighted deviates [MSWD] = 0.19) and 2335 ± 16 Ma (2σ, MSWD = 0.80). Biotite schist, which is interleaved locally with the quartz-sericite schist and is interpreted to be a basaltic-andesitic sill, yielded a younger zircon U-Pb upper concordia intercept age of 2191 ± 10 Ma (2σ, MSWD = 1.7). Five samples of granodiorite and granodiorite porphyry that intruded the schist sequence yielded similar zircon U-Pb ages, with a weighted mean upper concordia intercept age of 2182 ± 7 Ma (2σ, MSWD = 1.3). These results suggest that the volcanic sequence was deposited between ∼2.5 and 2.3 Ga and was intruded by basaltic-andesitic sills and a suite of granodiorite and granodiorite porphyry intrusions at ∼2.19 to 2.18 Ga.Two stages of copper mineralization are interpreted to have formed after pervasive sericite alteration of the felsic volcanic rocks. Stage 1 mineralization includes disseminated and deformed quartz veinlets containing chalcopyrite ± pyrite ± magnetite ± molybdenite associated with biotite ± K-feldspar alteration in granodiorite porphyry and schist. Stage 2 comprises undeformed quartz-chlorite-carbonate veins with bornite ± chalcopyrite ± magnetite associated with local chlorite and silicic alteration. Allanite crystals intergrown with chalcopyrite in the granodiorite porphyry yielded an approximate concordia U-Pb age of 2115 ± 31 Ma (2σ, MSWD = 2.3). Two molybdenite samples in a deformed quartz-chalcopyrite-molybdenite vein yielded Re-Os model ages of 2106 ± 9 and 2089 ± 9 Ma (2σ), consistent with previously published results.Hydrothermal monazite grains with Cu-Fe sulfide inclusions in the granodiorite porphyry, quartz-sericite schist, and undeformed chlorite-bornite-quartz veins yielded much younger U-Pb upper concordia intercept ages of 1832 ± 16 (2σ, MSWD = 0.48), 1810 ± 14 (2σ, MSWD = 0.92), and 1809 ± 12 Ma (2σ, MSWD = 0.38), respectively. The results are in agreement with four Re-Os model ages for pyrite mineral separates from undeformed quartz-sulfide veins, which yielded a weighted mean age of 1807 ± 4 Ma (2σ, n = 4, MSWD = 0.42). In contrast, hydrothermal rutile crystals in the quartz-sericite schist and biotite schist yielded a range of roughly concordant ages between 2.1 and 1.8 Ga, reflecting isotopic disturbance.We interpret these results to indicate original copper mineralization at ∼2.1 Ga that is significantly later than the granodiorite (∼2.18 Ga) and schists (∼2.5–2.2 Ga), followed by hydrothermal remobilization and metamorphism at ∼1.8 Ga. The metavolcanic and granodiorite porphyry host rocks, alteration styles, and disseminated and veinlet form of the earlier mineralization are strongly reminiscent of porphyry Cu deposits, and ages of ∼2.1 Ga have been reported for one intrusion and three volcanic rock samples from the district. The Tongkuangyu, therefore, represents one of the oldest known porphyry copper deposits. Remobilization of copper occurred at ∼1.8 Ga during the Zhongtiao orogeny.

Petrological and structural investigation of rocks around Igarra, southwestern Nigeria

Structural mapping and petrographic study carried out on the exposed Basement rocks of Igarra area, Southwestern Nigeria, have been used to infer the metamorphism, evolution and deformation history prevalent in the Igarra schist belt. The rocks exposed in the Igarra schist belt are mainly metasediments and intrusives. The metasediment comprises of inter-bedded quartz-biotite schist and minor bodies of quartzite, metaconglomerate, quartz-sericite schist and marble. The intrusives which cross-cut the metasediments in places consist of porphyritic-granite, aplite/pegmatite, syenite and subsidiary quartz vein. Petrographic analysis study involved megascopic and microscopic studies of structures in the rocks, while structural analysis entailed field based measurements and stereographic plots of structural elements of the metasediments. Two phases of metamorphism and deformation were inferred from two generations of foliation, S1 and S2 in that order. Metamorphic facies defined by index minerals assemblage indicated a low to medium grade metamorphism. Structural analysis of field data reveals a NNW-SSE trending foliation S2 that cut across an earlier foliation S1,generally in a N-S direction and a tight to isoclinal anticline plunge fold of the metasediments. The evolution of this belt can be related to sedimentary piles that were deformed and metamorphosed as a result of tectonic activities during the Paleoproteozoic and Neoproterozoic times, followed by the intrusion of granitoids and subsequent erosion and weathering of the rocks to produce the present topography.Keywords: Metasediments, petrography, metamorphism, structural mapping, Igarra, southwestern Nigeria

Hydrothermal gold mineralization and structural controls near May Hibey, Northwestern Tigray, Northern Ethiopia

Ezana Mining Development Company has recently reported presence of gold mineralization near May Hibey area, western Tigray, northern Ethiopia. It is in association with hydrothermal quartz veins within the Neoproterozoic low grade basement rocks, metavolcanics and metasedimentary rocks. Structural data suggests four phases of deformations and NE-SW trending foliation is the prominent one among others. Among different generations of veins, NNE, NS and NNW trending third generation quartz veins are gold-bearing and presence of a narrow shear zone with dextral sense of movement trending NW-SE is significant interms of mineralization. Hydrothermal alterations are dominated by chloritization and sericitization. Core samples from shear zone within the sericite-quartz schist and quartz porphyry rocks shows presence of pyrite, pyrrhotite, sphalerite, chalcopyrite, galena and gold in decreasing order of abundance. Gold mineralization is closely associated with the sericite and carbonization alteration zone. Based on mineral association, alteration, deformation, texture, and paragenetic scheme, it is suggested that the mineralization is a syn-orogenic variety formed in an island arc tectonic setting.Keywords: Quartz veins, Shear zones, Gold, Petrography, Geochemistry, MayHibey, Ethiopia.

Dating the Gaofan and Hutuo Groups – Targets to investigate the Paleoproterozoic Great Oxidation Event in North China

There are several sedimentary units in North China that are proposed to be associated with the Paleoproterozoic Great Oxidation Event (GOE) and/or subsequent events; however, few of them have been precisely dated. In this study, deposition age of the greenschist facies Gaofan and Hutuo Groups is determined. Zircon grains liberated from a tuff layer (metamorphosed to sericite-quartz schist) in the upper part of the Mohe Formation (the second of the three formations of the Gaofan Group) yield a weighted average 207Pb/206Pb age of 2186±8Ma (n=7, MSWD=1.3), representing time of deposition. This age and the detrital zircon U-Pb ages of the basal feldspar quartzite (meta-siltstone), as well as the initial deposition age of the unconformably overlying Hutuo Group, confine the deposition age of the Gaofan Group to 2350–2150Ma. This result negates the Gaofan Group as one subgroup of the 2560–2510Ma Wutai greenstone belt. Zircons from the Banlaoyao mafic sill (meta-diabase) that intruded the Dongye Subgroup of the Hutuo Group yield an upper intercept U-Pb age of 2057±25Ma (n=14, MSWD=1.3), representing time of crystallization. Considering the age of the basalt in the first formation of the Doucun Subgroup and the tuff in the first formation of the Dongye Subgroup, the deposition age of the Doucun and Dongye Subgroups of the Hutuo Group is confined to 2150–2090Ma and 2090–2060Ma, respectively. These age brackets, as well as the available carbon and nitrogen isotope data indicate that the Zhangxianbu Formation of the Gaofan Group possibly recorded the GOE; whereas the Mohe-Yaokouqian Formations of the Gaofan Group and the Doucun-Dongye Subgroups of the Hutuo Group recorded the subsequent Lomagundi-Jatuli Event (LJE). However, the Lomagundi-Jatuli carbon excursions are hardly distinguishable from the Gaofan Group and the Doucun Subgroup (Hutuo Group) as both units consist of little inorganic carbon but terrestrial clastic turbidites.

Genesis of the Kaladawan Fe–Mo ore field in Altyn, Xinjiang, China: Constraints from mineralogy and geochemistry

The Kaladawan Fe–Mo ore field in Altyn (Xinjiang Province, NW China) contains six Fe (–Mo) deposits, with total proven reserves of 60Mt Fe and 10,000t Mo. Tabular, lensoidal and stratiform orebodies occur in the Cambrian foliated marble, phyllite, carbonaceous slate, chlorite–sericite schist and quartz–sericite schist along the exocontact zone of the Kaladawan granite. Skarns are extensively developed and dominated by garnet, pyroxene, epidote, tremolite and actinolite, with minor chlorite, zoisite, quartz and calcite. Ore minerals are mainly magnetite and molybdenite. Five alteration and mineralization stages (I–V) were identified: the prograde (I) and retrograde (II) skarns are characterized by assemblages of garnet–pyroxene and epidote–tremolite–actinolite, respectively, intruded and replaced by mineral assemblages of magnetite–epidote–zoisite (III), quartz–sulfides (IV) and calcite–chlorite (V) in younging order. The Kaladawan garnet contains more andradite (61.2–94.4mol%) than grossularite (37.5–5.0mol%). Pyroxene is Mg-rich and Fe-poor, with an endmember range of 55.4–94.7mol% diopside and 42.5–4.7mol% hedenbergite. Amphibole comprises mainly tremolite and actinolite. The Kaladawan skarn mineral contents resemble typical skarn Fe and Mo deposits. In-situ LA-ICP-MS magnetite trace element analysis had identified unusually high Mg, Mo and Cr concentrations. The high Mo and the absence of molybdenite inclusions in magnetite suggest that the hydrothermal fluids may have been Mo-rich. The magnetite also contains similar (Ti+V) and (Al+Mn) values with typical skarn Fe deposits. Therefore, the Kaladawan Fe–Mo mineralization is best attributed to be skarn-type, and related to the Kaladawan granite intrusion.

Influence of confining pressure and impact loading on mechanical properties of amphibolite and sericite-quartz schist

In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confining pressure, two rocks are subjected to impact loadings with different strain rates and confining pressures by using split Hopkinson pressure bar equipment with a confining pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confining pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that: (1) The characteristics of two rocks in the ascent stage of the stress-strain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confining pressure increases. (2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confining pressure effects are obvious. (3) Due to the effect of confining pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice.

The Pinal Schist of southern Arizona: A Paleoproterozoic forearc complex with evidence of spreading ridge-trench interaction at ca. 1.65 Ga and a Proterozoic arc obduction event

The Pinal terrane of southern Arizona is composed mostly of quartz-sericite schists, meta-wackes, metavolcanic rocks, and granitoid and gneissic rocks, with minor meta-chert, meta-conglomerate, and carbonate rocks. Various tectonic settings have been suggested for the origin of this terrane. The existence of tectonic melanges within the terrane, the presence of granitic rocks in close proximity to the melanges, the presence of both oceanic and arc-like metavolcanic rocks within the terrane, the age distributions of igneous and meta-igneous rocks within the terrane, the deformational patterns within the terrane, and the width of the terrane all support a model in which the terrane was formed as a forearc-subduction complex that experienced a ridge subduction event at ca. 1.65 Ga. The Pinal terrane was likely the forearc-subduction complex to the Mazatzal arc terrane, which lies immediately to the north. Regional variations in the mineralogy of metavolcanic and metasedimentary rocks exposed within the terrane together with structural data suggest the terrane may have experienced an arc obduction event in the Proterozoic after the ridge subduction event. If it did, most of this arc terrane was eroded off the Pinal terrane in the 300 m.y. following the obduction event and prior to deposition of the Apache Group at ca. 1.32 Ga. There is a Paleoproterozoic arc terrane exposed in northern Mexico that may represent remnants of an obducted arc terrane. High-pressure–high-temperature metamorphic rocks (e.g., blueschists) have not been identified within the Pinal terrane.

Geology, C–H–O–S–Pb isotope systematics and geochronology of the Yindongpo gold deposit, Tongbai Mountains, central China: Implication for ore genesis

The Yindongpo gold deposit is located in the Weishancheng Au–Ag-dominated polymetallic ore belt in Tongbai Mountains, central China. The ore bodies are stratabound within carbonaceous quartz–sericite schists of the Neoproterozoic Waitoushan Group. The ore-forming process can be divided into three stages, represented by early barren quartz veins, middle polymetallic sulfide veinlets and late quartz–carbonate stockworks, with most ore minerals, such as pyrite, galena, native gold and electrum being formed in the middle stage. The average δ18Owater values changed from 9.7‰ in the early stage, through 4.9‰ in the middle stage, to −5.9‰ in the late stage, with the δD values ranging between −65‰ and −84‰. The δ13CCO2 values of ore fluids are between −3.7‰ and +6.7‰, with an average of 1.1‰. The H–O–C isotope systematics indicate that the ore fluids forming the Yindongpo gold deposit were probably initially sourced from a process of metamorphic devolatilization, and with time gradually mixed with meteoric water. The δ34S values range from −0.3‰ to +5.2‰, with peaks ranging from +1‰ to +4‰. Fourteen sulfide samples yield 206Pb/204Pb values of 16.990–17.216, 207Pb/204Pb of 15.419–15.612 and208Pb/204Pb of 38.251–38.861. Both S and Pb isotope ratios are similar to those of the main lithologies of the Waitoushan Group, but differ from other lithologic units and granitic batholiths in the Tongbai area, which suggest that the ore metals and fluids originated from the Waitoushan Group. The available K–Ar and 40Ar/39Ar ages indicate that the ore-forming process mainly took place in the period of 176–140Ma, during the transition from collisional compression to extension and after the closure of the oceanic seaway in the Qinling Orogen. The Yindongpo gold deposit is interpreted as a stratabound orogenic-style gold system formed during the transition phase from collisional compression to extension.The ore metals in the Waitoushan Group were extracted, transported and then accumulated in the carbonaceous sericite schist layer. The carbonaceous sericite schist layer, especially at the junction of collapsed anticline axis and fault structures, became the most favorable locus for the ore bodies.

Re-Os and U-Th-Pb dating of the Rochovce granite and its mineralization (Western Carpathians, Slovakia)

Abstract The subsurface Rochovce granite intrusion was emplaced into the contact zone between two principal tectonic units (the Veporic Unit and the Gemeric Unit) of the Central Western Carpathians (CWC), Slovakia. The Cretaceous age of this granite and its Mo-W mineralization is shown using two independent methods: U-Pb on zircon and Re-Os on molybdenite. The studied zircons have a typical homogeneous character with oscillatory zoning and scarce restite cores. SHRIMP U-Pb data provide an age of 81.5 ± 0.7 Ma, whereas restite cores suggest a latest Neoproterozoic-Ediacaran age (~565 Ma) source. Zircon εHf(81) values -5.2 to + 0.2 suggest a lower crustal source, whereas one from the Neoproterozoic core εHf(565)= + 7.4 call for the mantle influenced old precursor. Two molybdenite- bearing samples of very different character affirm a genetic relation between W-Mo mineralization and the Rochovce granite. One sample, a quartz-molybdenite vein from the exocontact (altered quartz-sericite schist of the Ochtiná Formation), provides a Re-Os age of 81.4 ± 0.3 Ma. The second molybdenite occurs as 1-2 mm disseminations in finegrained granite, and provides an age of 81.6 ± 0.3 Ma. Both Re-Os ages are identical within their 2-sigma analytical uncertainty and suggest rapid exhumation as a consequence of post-collisional, orogen-parallel extension and unroofing. The Rochovce granite represents the northernmost occurrence of Cretaceous calc-alkaline magmatism with Mo-W mineralization associated with the Alpine-Balkan-Carpathian-Dinaride metallogenic belt.

Experimental Study on Dynamic Mechanical Properties of Amphibolites, Sericite-quartz Schist and Sandstone under Impact Loadings

Abstract In order to investigate rock dynamic mechanical properties of amphibolites, sericite-quartz schist and sandstone under the different strain rates varying from 30 s -1 to 150 s -1 , the specimens were subjected to axial impact at different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter. The optimal experimental size of rock samples is verified by analyzing the stress equilibrium of cylindrical rock samples in different thicknesses. It has studied the mechanic properties of these three rocks which under impact loadings; and analysed the dynamic compressive strength, failure modes, energy dissipation variation with the strain-rate and the strain-rate hardening effect from the perspective of material microstructure. Experimental results show that the dynamic Young’s modulus of rock samples increase with strain-rate slightly. The dynamic failure modes of different rock samples are always different. When at a lower strain-rate, the damage of sandstone takes a peeling off the external radial tensile failure mode, but that of amphibolites takes axial splitting mode; when at a higher strain-rate, sandstone takes granular crushing failure mode, and that of amphibolites and of sericite-quartz schist take massive crushing mode. Significant strain-rate effect can be represented by a linear relation between the specific energy absorption and the strain-rate , or between the dynamic strength increase factor η and .

Experimental Study on Dynamic Mechanical Properties of Amphibolites, Sericite-quartz Schist and Sandstone under Impact Loadings

Abstract In order to investigate rock dynamic mechanical properties of amphibolites, sericite-quartz schist and sandstone under the different strain rates varying from 30 s -1 to 150 s -1 , the specimens were subjected to axial impact at different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter. The optimal experimental size of rock samples is verified by analyzing the stress equilibrium of cylindrical rock samples in different thicknesses. It has studied the mechanic properties of these three rocks which under impact loadings; and analysed the dynamic compressive strength, failure modes, energy dissipation variation with the strain-rate and the strain-rate hardening effect from the perspective of material microstructure. Experimental results show that the dynamic Young’s modulus of rock samples increase with strain-rate slightly. The dynamic failure modes of different rock samples are always different. When at a lower strain-rate, the damage of sandstone takes a peeling off the external radial tensile failure mode, but that of amphibolites takes axial splitting mode; when at a higher strain-rate, sandstone takes granular crushing failure mode, and that of amphibolites and of sericite-quartz schist take massive crushing mode. Significant strain-rate effect can be represented by a linear relation between the specific energy absorption and the strain-rate , or between the dynamic strength increase factor η and .

Experimental Study on Dynamic Mechanical Properties of Amphibolites, Sericite-quartz Schist and Sandstone under Impact Loadings

Abstract In order to investigate rock dynamic mechanical properties of amphibolites, sericite-quartz schist and sandstone under the different strain rates varying from 30 s -1 to 150 s -1 , the specimens were subjected to axial impact at different projectile speeds by using the split Hopkinson pressure bar (SHPB) of 100 mm in diameter. The optimal experimental size of rock samples is verified by analyzing the stress equilibrium of cylindrical rock samples in different thicknesses. It has studied the mechanic properties of these three rocks which under impact loadings; and analysed the dynamic compressive strength, failure modes, energy dissipation variation with the strain-rate and the strain-rate hardening effect from the perspective of material microstructure. Experimental results show that the dynamic Young's modulus of rock samples increase with strain-rate slightly. The dynamic failure modes of different rock samples are always different. When at a lower strain-rate, the damage of sandstone takes a peeling off the external radial tensile failure mode, but that of amphibolites takes axial splitting mode; when at a higher strain-rate, sandstone takes granular crushing failure mode, and that of amphibolites and of sericite-quartz schist take massive crushing mode. Significant strain-rate effect can be represented by a linear relation between the specific energy absorption and the strain-rate , or between the dynamic strength increase factor η and .