Granodiorite Intrusions Research Articles

Deformation mechanisms, mineral chemistry and zircon U-Pb geochronological constraints in the south Patos shear zone: implications for the crustal evolution of the Borborema Province, NE Brazil

The southern boundary of the Patos Shear Zone (PSZ) is characterized by mylonites resulting from the deformation of Paleoproterozoic basement gneisses, Neoproterozoic metavolcanic and metasedimentary rocks, granitic and granodioritic intrusions. Among the latter, the Santa Terezinha and Catingueira plutons show stretched shapes in agreement with the the shear zone’s regional trend. Recrystallized quartz grains in these plutons accommodate deformation by dislocation creep. The host banded gneisses show similar deformation structures to the plutons. Quartz crystallographic fabrics mainly record the activity of basal and prism slip planes with local contribution of rhomb planes, whilst feldspar clasts show evidence of intracrystalline deformation in the larger porphyroclasts. These characteristics suggest that shearing occurred at lower-amphibolite facies conditions. U-Pb zircon data for the Santa Terezinha pluton yields an age of 625 ± 7 Ma, which, coupled with the pluton elongated shape and microstructure, suggests that its emplacement was pre-kinematic in relation to the Patos shear zone. Post-emplacement elongation of the granite body occurred along the strike-slip trend. Such structural and geochronological constraints highlight the close association between magma emplacement and shear zone deformation during distinct stages of the Brasiliano-Pan-African orogeny in the Borborema Province.

Zircon U-Pb ages and provenance characteristics of the Zhiluo Formation sandstones and the formation background of the uranium deposit in Huangling area, Ordos Basin, China

The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin. This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area. The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The source rocks originated from a continental island arc environment in terms of tectonic setting. U-Pb ages of detrital zircons obtained can be roughly divided into three groups: 170–500 Ma, 1600–2050 Ma, and 2100–2650 Ma. Based on the characteristics of trace elements and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks (such as granodioritic intrusions) and metamorphic rocks (such as gneiss and granulite) in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block. Based on sedimentological and petrological results, it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction. The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area. Meanwhile, the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin. The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.©2021 China Geology Editorial Office.

Strontium isotopes in high- and low-Ge coals from the Shengli Coalfield, Inner Mongolia, northern China: New indicators for Ge source

The coal-hosted Ge deposit (Early Cretaceous) at Wulantuga, Inner Mongolia, northern China, is one of the largest Ge deposits in the world. Although the origin, modes of occurrence, and spatial distribution of Ge in this deposit have been investigated by several studies, the provenance and pathways of Ge from the source to the deposit are largely unknown. In this study, we investigated the 87Sr/86Sr values in the high-Ge coal of the Wulantuga deposit and the stratigraphically-equivalent low-Ge coal of the No. 1 Pit, both from the Shengli Coalfield, Inner Mongolia, northern China. In addition to an organic association, Sr and Ca in the high-Ge and low-Ge coals also occur in gypsum. The water-soluble Sr (i.e., in gypsum) in the high-Ge coal (Ge concentrations: 45–1170 ppm, 273 ppm on average, whole coal basis) has 87Sr/86Sr values in the range of 0.710411 to 0.710633 (with an average of 0.710478). In contrast, the low-Ge coal (Ge concentrations: up to 4.23 ppm, 0.45 ppm on average, whole coal basis) has lower 87Sr/86Sr values in two sub-groups, a low range of 0.709896–0.71005 (with an average of 0.709736) and a high range of 0.710173–0.710547 (with an average of 0.710329 and dominantly in the range of 0.710173–0.710406). The higher 87Sr/86Sr values in the high-Ge coals indicate that the highly-elevated concentration of Ge is associated with a local source of radiogenic Sr. The enrichment of Ge in the coal is due to several consecutive processes. Surface waters penetrated deeply into granite and dissolved at least partially more soluble phases of the granite. The Ge-rich solution flowed over ground or underground into the Shengli Coalfield and Ge precipitated in the peat, the precursor of the coal investigated in the coalfield. The 87Sr/86Sr values of the water-soluble fraction, the elemental compositions of high-Ge and low-Ge coals, and the geomorphological setting of the coalfield point to the Hercynian granodiorite intrusion on the nearby SE margin of the Shengli Coalfield as the primary source of Ge in the Wulantuga coal-hosted Ge deposit. In addition to serving as an indicator of the mode of formation of the coal-hosted Ge deposit, the 87Sr/86Sr values and their spatial distribution can provide an indication for the hydrological pathways of the mineralising fluid.

Alteration and structural features mapping in Kacho-Mesqal zone, Central Iran using ASTER remote sensing data for porphyry copper exploration

ABSTRACT Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite imagery was used to identify argillic, phyllic and propylitic alteration zones and mapping geological structural features for porphyry copper exploration in the Kacho-Mesqal zone, Urumieh- Dokhtar Magmatic Arc, Iran. The image processing techniques such as specialised band ratio, Selective Principal Component Analysis (SPCA), and Spectral Angle Mapping (SAM) image processing methods were implemented to the visible and near-infrared and shortwave infrared bands of ASTER. Results indicate that the argillic alteration zone is broadly distributed in the granodiorite intrusion, andesitic rock, tuff breccia and ignimbrite. Phyllic alteration is mainly mapped associated with sandstone and some parts of andesitic lithology. Propylitic alteration zone is identified in andesite, sandstone, shale and marl, dacite to rhyodacite, andesite-basalt, tuff and andesite lava and granodiorite intrusion. The fracture density map shows that the argillic alteration is mostly abundant in the high-density fracture zone, whereas propylitic and phyllic zones are located in moderate to low-density fracture zones. Consequently, high potential zones for copper mineralisation in the study area are identified within the high to moderate fracture density zones associated with argillic and assemblage of argillic, phyllic and propylitic alteration zones in granodiorite and andesite units.

Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

Abstract Granitoid rocks are universal in continental crust and are of special significance in understanding tectonic settings. This paper presents detailed zircon U-Pb dating, Hf isotope, whole-rock geochemistry, and Sr-Nd-Pb isotope analyses, and mineralogy of two Ordovician granitoid intrusions and one quartz diorite intrusion in Western Kunlun, NW Tibetan Plateau. The Yutian Complex is composed of diverse rock suites, including monzogabbros, quartz monzodiorites, monzogranites, and monzodioritic enclaves. These suites have similar rock formation ages (447–440 Ma) and minerals, e.g., amphibole grains from different suites belonging to pargasite. Moreover, they exhibit geochemical similarities, such as broadly parallel trace-element patterns characterized by enrichments in light rare earth elements and large ion lithophile elements, and depletions in high field strength elements, which are typical features of arc rocks. Furthermore, the studied samples display homogeneous zircon Hf values, e.g., εHf(t) = −1 to −3, and whole-rock isotopic compositions, e.g., εNd(t) = −4 to −6. Thus, they were most likely derived from a mantle wedge enriched by subducted sediments and fluids, which then evolved into different suites through fractional crystallization of hornblende and plagioclase. The ca. 440 Ma North Yutian quartz diorite intrusion, with an average of εHf(t) value of −6, was a product of the partial melting of mafic lower crust through slightly fractional crystallization of hornblende. In contrast, the ca. 470 Ma Aqiang granodiorite intrusion has εHf(t) values varying from −5 and −2, but it has heterogeneous petrological and geochemical features. It is considered to be a product of the partial melting of the overriding mantle wedge modified by fluids derived from the subducted Proto-Tethys slab and some mixed crustal materials. The Aqiang samples belong to the slightly fractionated I-type series, but they have variable alumina saturation index (ASI = molar Al2O3/[CaO – 3.33 × P2O5 + Na2O + K2O]) values (0.74–1.03) due to variable peraluminous biotite contents. The different suites in the Yutian Complex display low ASI values (<1) controlled by sources and fractional crystallization. The Yutian Complex and the North Yutian intrusion were emplaced during the southward subduction of the Proto-Tethys oceanic lithosphere, and the Aqiang intrusion was emplaced in response to the northward subduction.

Contribution to the understanding of the Pinheiro Machado Complex (Dom Feliciano Belt, Brazil): A study of textures, mineral chemistry, and crystallization conditions

This article presents textures, mineral chemistry, and geothermobarometric data for the southeastern Pinheiro Machado Complex rocks (PMC), eastern domain of the Dom Feliciano Belt, Rio Grande do Sul, Brazil. The PMC is composed by comagmatic intrusions of quartz diorite, tonalite, and granodiorite with medium‐ to fine‐grained equigranular and medium‐grained inequigranular textures with subordinate alkali‐feldspar macrocrystals. Partial melting features are observed in the comagmatic as melt pools and melt films. Amphibolite xenoliths also occur, presenting sharp‐angled to rounded contacts with the intrusions and evidences of partial assimilation, marked by mafic schlierens. Electron probe microanalyzer punctual analyses were used to classify amphibole, plagioclase, biotite, epidote, and titanite, as well as for the calculations of the crystallization P–T conditions. Amphiboles consist of pargasite for the comagmatic intrusions, and Mg‐hornblende for the amphibolite. Plagioclase ranges from oligoclase to andesine (An15‐40) in both units. Biotite corresponds to annite, with Fe/(Fe + Mg) > 0.3. The epidote has mostly magmatic characteristics in the comagmatic intrusions, with pistacite content 25–30%. Titanite has two distinct textures, titanite I is well formed, subhedral to euhedral, with up to 3 mm; while titanite II is anhedral with size >1 mm and rounded shapes, being both chemically homogeneous. The estimated P–T conditions for the amphibolite crystallization, using plagioclase‐hornblende geothermometer are 650–850°C and 3.62–4.95 kbar, whereas the conditions from the comagmatic intrusions are 714–871°C and 4.44–6.10 kbar. In the mineral phases there is a prevalence in the recrystallization field between subgrain rotation (SGR) and grain boundary migration (GBM) in submagmatic flow. These new data indicate that possibly at the end of PMC crystallization, late magmatic fluids caused re‐equilibrium of mineral phases, mainly in biotite and feldspars. Finally, we suggest that the PMC is the result of continuous and repeated comagmatic intrusions in a continental magmatic arc setting at a depth of 20–30 km in an amphibolitic continental crust.

In situ geochemistry of dyke−marble interfaces obtained by portable X-ray fluorescence (pXRF) spectroscopy: Implications for sources of ore-forming materials in the Baiyinnuo'er Zn–Pb deposit, inner Mongolia, China

In situ analysis performed by portable X-ray fluorescence (pXRF) spectroscopy was used to measure two different contact interfaces of dyke and marble in the Baiyinnuo'er Zn–Pb deposit located in Inner Mongolia, China. The limit of detection (LOD) standardisation method was used to assess pXRF readings through dividing readings into low, medium and high concentrations, and readings were screened according to the concentration range distribution. Spatial trend analysis and enrichment factor calculation were used for data processing. In both profiles of quartz porphyry−marble (Q−M) and granodiorite−marble (G−M), high values of Ca and Mg, and Si, Al and K, respectively, could be used to distinguish the distribution of marble and dykes. However, there were significant differences in the distributions of ore-forming elements between the two profiles. No ore-forming elements were enriched near the contact interface of the Q−M profile, but all ore-forming elements, such as Zn, Pb, Cu and Fe, were significantly enriched in the skarns located between granodiorite and marble. Therefore, the intrusion of granodiorite resulted in the enrichment of ore-forming elements, and provided metals for mineralisation. Based on the results of the calculated enrichment factor for the G−M profile, the enrichment degree of selected elements in descending order was Pb, Zn > Ca > Fe > Al, Si > K in skarns relative to granodiorite, and Pb, Fe > Si, Al > Zn > K > Ca in skarns relative to marble. Zn and Pb were enriched in skarns relative to granodiorite but partially depleted relative to marble, indicating the high background Zn and Pb in marble; therefore, marble could provide at least part of the Zn and Pb. As a consequence, the intrusion of granodiorite resulted in skarnisation and mineralisation, and introduced ore-forming elements including Zn, Pb, Cu and Fe, but marble also provided at least part of the Zn and Pb, and the deposit was considered to be a skarn Zn–Pb deposit. In situ geochemical analysis at the outcrop scale is a useful approach for research into geological processes including skarnisation and mineralisation, as well as determining the source of ore-forming materials.

Late Miocene to Pliocene crustal extension and lithospheric delamination revealed from the ~5 Ma Palopo granodioritic intrusion in Western Sulawesi, Indonesia

Recent studies have revealed that following collision between the Western Sulawesi and Sula Spur microcontinents during the early to middle Miocene, the Western Sulawesi microcontinent subsequently underwent extension. However, the geodynamic process that resulted in extension is unknown. The petrogenesis of late Miocene to Pliocene granitoids in the region provides insights to the mechanism of extension. To achieve this goal, we studied the Palopo granodioritic intrusion, a well-exposed representative pluton that crops out along the Palu–Koro Fault. Zircon U–Pb dating indicates a 4.8–4.7 ± 0.1 Ma crystallization age for the pluton. Compared with arc igneous rocks, the pluton has high Sr contents and low Y and Yb contents, with relatively high Sr/Y and LaN/YbN ratios. These geochemical signatures are similar to those of typical adakites. The samples exhibit high MgO (1.60–2.54 wt%), Cr (46–65 ppm), and Ni (14.1–19.0 ppm) contents relative to adakitic rocks derived from thickened lower crust. In addition, negative εHf(t) (−9.7 to −5.5) and εNd(t) (−8.5 to −11.1) values, together with relatively low 143Nd/144Nd and high initial 87Sr/86Sr ratios, reflect an origin through recycling of ancient crustal materials, which is clearly different from adakites derived from melting of a subducting slab. The most plausible mechanism for generation of the late Miocene–Pliocene adakitic granodiorites in the Western Sulawesi microcontinent is partial melting of delaminated lower crust that interacted with the mantle. We propose that the late Miocene to Pliocene crustal extension in the Western Sulawesi microcontinent was triggered by delamination of pre-existing thickened lithosphere.

Physico-chemical parameters of Neoarchean syntectonic magmatism: The example of the Muscocho Pluton, Abitibi Subprovince

The Muscocho Pluton is one of a number of syntectonic Neoarchean granodiorite intrusions formed during the main deformation phase in the Abitibi Subprovince that lead to stabilization of the Superior craton. Such magma locally are associated with magmatic-hydrothermal styles of mineralization, interpreted by some works to reflect intrusion-related gold systems (IRGS). Determining whether magmas can transport enough Au to fertilize the upper crust during this tectonomagmatic interval requires insights into physico-chemical parameters such as pressure, temperature, and oxygen fugacity (ƒO2). The ƒO2 parameter is particularly important because it affects S-speciation and S-solubility, which correlates with Au-solubility in magmas. Retrieving such parameters from the metamorphosed, locally hydrothermally altered, and generally deformed Neoarchean rocks is particularly challenging. As such, this contribution uses fresh to altered granodiorites of the Muscocho Pluton, a 16 km diameter granodiorite intrusion spatially associated with polymetallic mineralization, to evaluate whether physico-chemical parameters can be retrieved from ancient altered rocks based on amphibole, apatite, and zircon chemistry. This study also has implications for the origins of the Muscocho Pluton, which ascended slowly toward the upper crust as a single pulse of evolved magma and became emplaced at about 12 km depth. The magma had an ƒO2 above the Ni/NiO solid oxygen buffer (NNO + 1), which is not considered optimal for Au transportation. The magma also formed a deep intrusion unable to provide magmatic fluids to trigger an efficient hydrothermal system. This study provides the basis for a systematic evaluation of the physico-chemical conditions within which syntectonic magmas evolved in the upper crust. Knowledge of these physico-chemical conditions are necessary to better constrain the IRGS metallogenic model.

Mineralogy and character of the Liikavaara Östra Cu-(W-Au) deposit, northern Sweden

ABSTRACT The Liikavaara Östra Cu-(W-Au) deposit is situated close to the operating Aitik Cu-Au mine in northern Sweden. It is scheduled for production in 2023. Modern geological descriptions of the deposit are lacking though knowledge of geological and mineralogical details prior to operation is beneficial to avoid surprises. In this study, petrological, mineralogical and geochemical investigations of the wall rocks, host rock and mineralisation, and zircon U-Pb analysis of a footwall granodioritic intrusion were carried out. The mineralisation is hosted by quartz±tourmaline-calcite veins, calcite veins and aplite dykes that cross-cut biotite-amphibole schists and gneisses. The wall rocks to the ore are metavolcaniclastic rocks of basaltic to andesitic composition. A granodiorite intrusion occurs in the footwall. The mineralisation is mainly chalcopyrite, pyrrhotite and pyrite with some sphalerite, galena, scheelite, molybdenite and magnetite. It shows slight enrichments in Au, Ag and Bi. Gold and Ag occur as electrum and Ag also in hessite and an Ag-sulphide. The Bi mineralogy includes native Bi, Bi-tellurides and Bi-sulphides. These minerals are found as inclusions, along the borders of and in cracks in chalcopyrite, pyrite, pyrrhotite, sphalerite, molybdenite and quartz. The footwall granodiorite intrusion was dated at 1.87 Ga. It is suggested here to be the source for ore genesis based on its spatial relation to the mineralisation, as well as on high-salinity fluids and metal composition of the ore. The aplite dykes may have acted as pathways for the magmatic hydrothermal fluids that carried the metals from the intrusion to the host rock.

Geochemical discrimination of intrusions in the Choran Cu[sbnd]Au deposit, Iran, using silicate chemistry

The Choran CuAu deposit is located 70 km of Bardsir in the southern part of Urumieh-Dokhtar magmatic belt (UDMB). In this area, mineralization is associated with Oligocene –Miocene quartz diorite and granodiorite intrusions emplaced within Eocene volcanic–pyroclastic – sedimentary sequences. Main hydrothermal alterations in the Choran region include sodic-potassic and potassic as well as phyllic, alunite and kaolinite which extended mostly in the granodiorite. Mineralizations at the Choran deposit involve pyrite, arsenopyrite, chalcopyrite, chalcocite, covellite and sphalerite. The composition of the plagioclase in the granodiorite and quartz diorite rocks ranges from albite (66.8 to 48.7) and (64.8 to 51.4) respectively. Also, Al/(Ca + Na + K) ratios of plagioclase in granodiorite samples (average; 1.50) are higher than that of quartz diorite intrusions (average; 1.33) which is analogous to those reported previously for mineralized porphyry systems. All studied primary and re-equilibrated biotites are collectively clustered in the Mg-biotite field. However, based on the log (XMg/XFe) versus log (XF/XOH) of biotite, granodiorite units are associated with I-type moderately crustal contaminated (I-MC) suite, whereas quartz diorite biotites represent I-type weakly crustal contaminated (I-WC) character. Comparison of biotite halogen contents indicates that F and Cl values increase from quartz diorite to granodiorite intrusions. Importantly, biotite thermometry of granodiorite and quartz diorite samples indicate temperatures of <400 °C (quartz diorite; average 340 °C, granodiorite; average 379 °C) which are overlapped with temperature of sulfide mineralization in the porphyry systems (<400 °C). Totally, through assessing the key factors of mineralization using silicate chemistry, it is proved that granodiorite units have higher potential to form porphyry-style sulfide mineralization in the Choran deposit.

Geological and mineralogical constraints on the genesis of the Bilihe gold deposit in Inner Mongolia, China

The Bilihe gold deposit is a rare example that economical gold mineralization occurred in unidirectional solidification textures (UST) quartz at the cupola of middle Permian granodioritic intrusion. However, there is a key dispute about whether gold precipitated from low-diffusion silicate melt or high-activity fluid phase. In this paper, based on in-situ trace elements analyzing, SEM-CL mapping, and infra-red and Raman spectroscopy, the magmatic fluids are supposed to play a critical role in the gold mineralization by metal extraction from below magma at magmatic-hydrothermal transition stage. At Bilihe, the UST quartz represents the most fertile unit. Statistic results show the quartz–K-feldspar (KV) and gray banded quartz veins (GBV) also host about 22–27% of total reserves. A decreasing trend in Au/Ag, and Au/S, but elevated Au/Cu ratios of gold compositions indicate a relatively continuous fluid evolution in the Bilihe system. Petrography and spectroscopy studies show that the Bilihe UST quartz can be divided into two different domains, gold-rich brownish and barren colorless zones. The former can contain more water, occurring as tiny fluid inclusion or as structural OH– in muscovite, corresponding to sector CL zones (UQ1) or euhedral oscillatory bands (UQ2). The latter usually contain melt inclusions and correspond to obscure CL-textures (UQ3). Besides, the LA-ICP-MS trace elements show that there is a significant decreasing trends on fluid-mobile elements (e.g., K, Fe, B, and Li) from UQ1 over UQ2 to UQ3. In particular, the trace elements in UQ3 show greater affinity with magmatic quartz phenocrysts but with higher Ge, B, and Li contents, and higher Ge/Ti and Ge/Al, but lower Li/Ti ratios, indicating a highly evolved and fluid-rich environment. Based on previous model, we consider that the Bilihe UST quartz grew in the variable growth mediums, namely fluctuant alternation between fluid-dominant pocket (for UQ1 + UQ2) and silicate melt phase (for UQ3) near the melt-fluid interface at the apex of magma body. The relatively H2O-poor nature of parent magma is an important factor to cause the specific crystal growth environment. Mineral thermobarometers demonstrate that the parent magma from deep reservoir has experienced a significant ascent or decompression (from ~ 3–5 kbar to ~ 0.5–1.8 kbar). In addition, high fluxing volatiles, such as B, F and P, effectively protract magma crystallization to form highly evolved melt, and finally resulting in water saturation at shallow level. Thus, gold saturation might reach in earlier exsolving low-salinity fluids at low pressure (as low as 0.5 kbar) and high temperature (~660–700 °C) condition. Then voluminous fluids get release accompanying with hydrofracturing, and some gold sequentially precipitate in the KV with fluids cooling (<550 °C) and later in the GBV with further cooling and flashing during transition from lithostatic to hydrostatic loads. With increasing sulfur fugacity by fluid condensation and further cooling in fluid temperature, secondary gold can precipitate with possible Cu-(Fe) or As-Sb sulfides associated with pervasive intermediate argillic alteration, which intensively overprinted on earlier potassic alteration zone.

Formation of the Cretaceous skarn Cu–Au deposits of the southern Gangdese belt, Tibet: Case studies of the Kelu and Sangbujiala deposits

Mesozoic subduction of Neo-Tethyan oceanic crust caused magmatism that formed numerous Jurassic and Cretaceous intrusions within the southern Gangdese belt of Tibet. These intrusions are associated with the formation of giant Jurassic Xiongcun porphyry Cu deposits, but the prospectivity of other Cretaceous intrusions in this area remains unclear. This study presents new molybdenite Re–Os ages for the Kelu and Sangbujiala Cu–Au skarn deposits within the southern Gangdese belt as well as new geochemical, zircon U–Pb geochronological, and Sr–Nd–Hf isotopic data for the intrusions associated with these deposits. These new data indicate that (1) the Kelu deposit formed at ca. 92 Ma, coeval with emplacement of the diorite and biotite granodiorite intrusions (ca. 92–90 Ma) in this area, and (2) the Sangbujiala deposit formed at ca. 95 Ma, contemporaneous with emplacement of the mineralized biotite granodiorite (ca. 95–92 Ma) in this area. These data suggest that the skarn Cu–Au mineralization in this area formed as a result of Cretaceous magmatism in the southern Gangdese belt. The intrusions associated with the Kelu and Sangbujiala deposits have adakitic affinities with low contents of Y and heavy rare-earth elements and high Sr/Y ratios (22.4–123). These intrusions also have more primitive Sr–Nd isotopic compositions (εNd(t) = 3.99–4.81, (87Sr/86Sr)i = 0.7040–0.7044), lower εHf(t) values (8.0–13.18), and higher zircon EuN/Eu* values (mean of 0.50) than those of contemporaneous but barren adakitic intrusions in this region. This suggests that the mineralization-related intrusions were oxidized and formed from magmas that were generated predominantly by partial melting of subducted Neo-Tethyan slab material without any significant crustal contamination or assimilation of sedimentary material. However, these intrusions contain elevated Th, Ni, and Cr contents, and have high Mg# ratios (43.4–56.9), suggesting that they formed from magmas that interacted with metasomatized mantle wedge peridotite material. Combining our new data with the results of previous research suggests that the southern Gangdese belt records two stages of Cu–Au mineralization related to Neo-Tethyan subduction. The first stage generated the large Xiongcun porphyry Cu–Au deposit and was associated with normal subduction during the Jurassic, whereas the second stage was associated with the formation of the Kelu and Sangbujiala skarn deposits during Cretaceous slab rollback.

Investigating the Irregular Localization of Skarn Orebodies by Computational Modeling in the Fenghuangshan Ore Field, Tongling District, Anhui Province, China

The localization patterns and mechanisms of orebody formation are critical in understanding and exploring for mineral deposits. Skarn ore deposits are especially difficult to study because of their complex features. The Fenghuangshan ore field is a maturely explored skarn copper ore field with many underground workings that reveal the skarn orebodies and related geological context in detail. This situation enables us to use computational modeling to investigate the irregular localization pattern of the skarn orebodies and their origin. Our 3D geometric modeling results show that the skarn orebodies are irregularly localized along the intrusion contact zone and that the irregular localization pattern is closely related to the topography and orientation of the contact zone. The largest orebodies and dominant reserves occur in the western contact zone (WCZ), mainly in the southern segment, where the contact zone is most concave (toward the intrusion). The thicknesses of the major orebodies in the WCZ are correlated with the Gaussian curvature of the contact surface. To investigate the localization mechanism of such irregular orebodies, we use numerical dynamic modeling to study the intrusion cooling process, which is critical for skarn orebody formation. The model consisted of a granodiorite intrusion and carbonate wall rocks, and it was ran on the FLAC3D platform to test three different scenarios: (1) syn-extensional cooling, which is the likely regional tectonic condition during the mineralization period; (2) syn-compressional cooling; and (3) cooling with no tectonic load. The dynamic modeling results for these three scenarios are distinctly different. Only the first scenario (NE–SW extension) can produce large-scale maximum dilation zones with a distribution pattern similar to that of the orebodies. As the maximum dilation zones are favorable for the formation of skarn ores, we conclude that the tectonic phase is also a critical constraint condition for the irregular localization of skarn orebodies.

The Role of Magma Mixing in Generating Granodioritic Intrusions Related to Cu–W Mineralization: A Case Study from Qiaomaishan Deposit, Eastern China

The newly exploited Qiaomaishan Cu−W deposit, located in the Xuancheng ore district in the MLYRB, is a middle-sized Cu–W skarn-type polymetallic deposit. As Cu–W mineralization is a rare and uncommon type in the Middle-Lower Yangtze River Belt (MLYRB), few studies have been carried out, and the geochemical characteristics and petrogenesis of Qiaomaishan intrusive rocks related to Cu–W mineralization are not well documented. We studied two types of ore-bearing intrusive rocks in the Qiaomaishan region, i.e., pure granodiorite porphyry and granodiorite porphyry with mafic microgranular enclaves (MMEs). Age characterization using zircon LA–ICP–MS showed that they were formed almost simultaneously, around 134.9 to 135.1 Ma. Granodiorite porphyries are high Mg# adakites, characterized by high-K calc-alkaline and metaluminous features that are enriched in LILEs (e.g., Sr and Ba) and LREEs, but depleted in HFSEs (e.g., Nb, Ta, and Ti) and HREEs. Moreover, they have enriched Sr–Nd–Hf isotopic compositions (with whole-rock (87Sr/86Sr)i ratios (0.706666−0.706714), negative εNd(t) values of −9.1 to −8.6, negative zircon εHf(t) values of −12.2 to −6.7, and two-stage Hf model ages (TDM2) between 1.5 and 2.0 Ga). However, compared to host rocks, the granodiorite porphyry with MMEs shows variable geochemical compositions, e.g., high Mg#, Cr, Ni, and V contents and enriched with LILEs. In addition, they have more depleted ISr, εNd(t), and εHf(t) values (0.706025 to 0.706269, −6.4 to −7.4, and −10.6 to −5.7, respectively), overlapping with regions of Early Cretaceous mafic rocks derived from enriched lithospheric mantle in the MLYRB. Coupled with significant disequilibrium textures and geochemical features of host rocks and MMEs, we propose that those rocks have resulted from mixing the felsic lower crust-derived magma and the mafic magma generated from the enriched mantle. The mixed magmas subsequently rose to shallow crust to form the ore-bearing rocks and facilitate Cu–W mineralization.

Geology, geochronology, and S-Pb-Os geochemistry of the Alastuo gold deposit, West Tianshan, NW China

The Alastuo gold deposit, located in the Narati region of the Chinese West Tianshan, is a newly discovered gold deposit within the world-class Tianshan gold belt. The gold mineralization is hosted by an Early Carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal North Narati Fault. The deposit consists of auriferous alteration assemblages and minor vein ores. Field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz, chlorite, epidote, pyrite, and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation. The temperature range of gold precipitation is estimated to be 280–330 °C using chlorite geothermometry. Ten auriferous pyrite samples yielded a well-defined Re-Os isochron age of 325 ± 3 Ma and two sericite samples yielded plateau-like 40Ar/39Ar ages of 321.7 ± 3.0 Ma and 321.2 ± 2.8 Ma. These consistent ages suggest that the gold mineralization in the Narati region was emplaced in a transitional regime from subduction to continental collision between the Tarim block and Middle Tianshan terrane (325–310 Ma), rather than during the post-collisional stage as in most part of the Tianshan gold belt. Gold-bearing pyrite has an initial Osi value of 0.7 ± 0.1 and lead isotopes ratios of 17.897 to 18.723 for 206Pb/204Pb, 15.474 to 15.643 for 207Pb/204Pb, and 37.522 to 38.299 for 208Pb/204Pb, while samples of pyrite, galena, and sphalerite have 34SV-CDT of +1.9 to +7.8‰. The isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks. The mineralization styles, structural controls, metal and sulfur sources, and the timing of gold mineralization with respect to the orogenic event all suggest that the Alastuo gold deposit represents an orogenic type deposit. This newly recognized Carboniferous orogenic gold mineralization event calls for a re-evaluation of the gold metallogeny in the Middle Tianshan.

Occurrence of wolfram, copper, cobalt and gold mineralization in the area of the Argentine Islands (West Antarctica)

Objective. The objective of our research was to search for manifestations of ore mineralization on the Roca and Cruls islands in the Argentine Islands, West Antarctica. Methods. Samples of rocks with the manifestation of ore mineralization were taken in the field routes. Silicate analysis of the rocks was carried out using the wet chemistry method in M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the National Academy of Sciences of Ukraine (IGMOF of NAS of Ukraine). The X-ray diffraction analysis of samples was carried out using a DRON-2 diffractometer, with copper radiation (СuКα = 1.54178A). The samples were surveyed in the 4—65° 2θ interval of angles, with a scan step of 0.1 degr. / min. For mineral diagnostics, the catalog of reference samples of the PDF-2 database (International Diffraction Data Center, ICDD) 2003. The chemical composition of minerals was examined using a JXA-733 X-ray microanalyzer (Jeol, Japan) using wave and energy-dispersion spectrometers. Contents of trace elements in the rocks were determined using the ICP-MS and quantitative spectral analysis methods. The validity of analyses was checked by means of determination of international and Russian reference samples GSP-2, VM, SGD-1А, ST-1.Concentration measuring errors were 3 to 5 wt. % for most elements. The quantitative spectrum analysis was carried out in IGMOF of NAS of Ukraine. Petrographic studies of rock sections were carried out using a MIN-8 polarized-light microscope. Results. Wolfram, copper, zinc, and lead were found in the minor intrusion of lamprophyres in the Andes complex granodiorites, on a small island of the Roca Islands. This semi-ring-shaped minor intrusion up to 0.5 m thick rooted in the not yet crystallized granodiorite intrusion. The dip angle of the minor intrusion is about 70°. It showed tungsten (28.7 g/t), copper (445 g/t), zinc (207 g/t), and lead (123 g/t) mineralization. In the eastern part of one of the Cruls Islands, a steep (dip azimuth NW 345°, angle 82°) tectonic zone up to 10 m wide was studied. Three metasomatic belts, one of which is up to 0.5 m thick, are associated with this zone. Metasomatites include pyrite-plagioclase rocks, epidosites and pyrite-epidote rocks, which have been formed due to hydrothermal and metasomatic changes of granodioritic tectonic breccia. The occurrence of cobalt (800 g/t), copper (200 g/t) and gold (up to 0.3 g/t) has beendiscovered. In these metasomatites, magnetite, pyrite, copper pyrite and pyrrhotite are available. Cobalt is present as magnetitic and pyritic impurities. Conclusions. During geological surveys in 2010 and 2012 the mineralization of wolfram, copper, lead, cobalt and gold was first discovered. The ore mineralization of such genesis was previously unknown in this area. The data obtained allow clarifying of perspectives of exploration activities in West Antarctica.

Linkage of distal vein–type Au mineralization in carbonate rocks with Cu–Au skarn mineralization in the Fengshan area, Eastern China: Mineralogy and stable isotope geochemistry

Numerous limestone–hosted vein–type Au deposits (12 million tonnes at 5.0 g/t Au) are located peripheral to Cu–Au skarn deposits around the Late Jurassic granodiorite intrusions in the Fengshan area, Middle–Lower Yangtze River metallogenic belt, Eastern China. Both the Cu–Au skarn and distal vein–type Au deposits have a complex mineral assemblage, consisting of base metal sulfides, sulfosalts and Au–Ag–(Tl) telluride minerals. In the Cu–Au skarn deposits, grains of electrum, Au–Ag tellurides (hessite and petzite) coexist with Bi–Te minerals (native bismuth, tetradymite, Phase C, and aikinite), sulfides (chalcopyrite, sphalerite, and galena), occurring as grain aggregates or veinlets. In the distal vein–type Au deposits, fine–grained Au–Ag–Tl tellurides (calaverite, petzite, hessite, and Tl–bearing Au telluride) occur as ore minerals in assemblages of sulfides, and carbonate minerals. The mineralogical Bi–Te signature characterizes the skarn assemblages, while the Te–Tl signature is typical of the distal vein–type Au mineralization.Textural relations and mineral assemblages allow the recognition of five generations of hydrothermal carbonate: (1) Cu sulfides and tellurides–bearing calcite assemblages; (2) sphalerite, galena and tellurides–bearing dolomite assemblages; (3) sericite, quartz and tellurides–bearing carbonate veinlets; (4) realgar and fluorite–bearing carbonate veinlets; (5) pure calcite veinlets. Electron microprobe analysis indicates that the tellurides–bearing, ore–related carbonate contains variable Mn content (up to 80 mol.% MnCO3).The C–O isotope compositions of carbonate from the Cu–Au skarn mineralization, to the carbonate–replacement Pb–Zn and distal vein–type Au mineralization, and to the post–ore, realgar–bearing veinlets in the country rocks display a tendency towards heavier isotopic compositions with time, which could be best interpreted as the effect of fluid–rock interaction between magmatic fluid and the Triassic carbonate host rocks. New S isotope data on sulfate minerals (anhydrite, gypsum, and celestite), and C–O isotopic data suggest a common magmatic fluid source for both skarn and distal vein–type mineralization.

Busur Magmatik Granit Tantan-Nagan Sebagai Potensi REE Di Jambi

ABSTRAK &#x0D; REE (Rare Earth Element) atau unsur-unsur tanah jarang adalah mineral yang mengandung salah satu ataupun lebih unsur yang terdapat dalam kelompok 17 elemen kimia, kelompok ini terdiri dari kelompok kimia lanthanide (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium) ditambahkan dengan scandium dan yttrium. Pada era Industri 4.0 atau industri modern REE (Rare Earth Element) merupakan komoditi yang sangat strategis, pemanfaatan unsur tanah jarang sangat dibutuhkan dalam berbagai macam bidang mulai dari industri elektronik, telekomunikasi, industri transportasi modern dan masih banyak lagi. Keterdapatan REE (Rare Earth Element) di Jambi-Sumatra terjadi sejak masa Mesozoikum Awal yaitu diawali dengan pembentukan Formasi Granit Tantan hingga masa Kenozoikum berupa pembentukan Formasi Granit Nagan. Lokasi penelitian berada di Sungai Manau, Kabupaten Merangin yang merupakan bagian dari busur magmatik Sunda yang tersusun oleh inrusi batuan plutonik granodiorit dengan xenolit berupa andesit, micro diorit dan diorit pada Formasi Tantan dan Intrusi batuan plutonik Granit, Granodiorit dan Adamelit pada Formasi Nagan. Hal ini dilakukan karena pembentukan endapan mineral unsur REE (Rare Earth Element) sangat berasosiasi dengan pendinginan batuan beku plutonik.Tujuan dari penelitian ini adalah untuk mengetahui kondisi Geologi Daerah penelitian dan hubungannya terhadap keterdapatan REE (Rare Earth Element) dan mengetahui Potensi REE yang terdapat pada Formasi Tantan dan Formasi Nagan yang ada di Kabupaten Merangin, Provinsi Jambi. Kata kunci: Potensi, REE, Unsur Tanah Jarang.

Hydrogeological Features of Geothermal Waters in Havran (Balıkesir), Turkey

In this study, geothermal waters of Havran were studied in detail. In the area, Karakaya formation in Early Triassic age is the basement consisting volcanic and sedimentary rocks such as of basalts, mudstones, and radiolarites in which there are intercalations of limestone, sandstones and conglomerates. Granodiorite intrusions in Oligocene to Miocene age occur in association with intense volcanic events in the area. From Upper Oligocene to Early Miocene, andesitic and dacitic pyroclastics occur due to intensively volcanism in the area. Later, lacustrine sediments consisting of conglomerates, sandstones, claystones, marls and limestones form from Middle to Upper Miocene. Geothermal waters in the area of Havran are of Na-Ca-(SO4)-HCO3, Na-(SO4)-HCO3 and Na-SO4 type. The geothermal waters display immature waters and were represented within this study as a hydrogeological model.