Andesitic Tuff Research Articles

Lithological Control to the Gold Mineralization in the Main Ridge Complex of the Bakan Gold District, Northern Sulawesi, Indonesia

Abstract Main Ridge complex is characterized by prominent high sulfidation epithermal-style mineralization with windows of porphyry style mineralization in the deeper zone. Several lithologic features play important controlling role in the occurrences of those mineralization. The oldest rock observed in the Main Ridge complex is unmineralized hornblende diorite (IDO-1) which encompasses the whole Bakan district. Several late intrusive stocks were concealed below the current topographic as mentioned as the microdiorite (IDO-2) and quartz diorite (IDO-3) in which the latter exhibits windows of porphyry-style mineralization. Those intrusive units were then covered by two unconformable volcanic tuff sequences which are andesitic tuff and dacitic tuff in compositions. Dacitic tuff is more favourable unit for gold mineralization compared to andesitic tuff which shown by near-surface ‘mushroom-like’ deposit form. In more peripheral area, the mineralization is also controlled by the bedding features of dacitic tuff which underlain by the less-mineralized andesitic tuff. In the latest stage, diatreme breccia cut all the lithologic units and becomes the most favourable host rock in sub-vertical deposit form. The comprehensive understanding of the lithological features is important to understand the mineralization control for further exploration target.

Preliminary Conceptual Model of Hydrogeological System in The Pandanduri Dam and its Surrounding Area on the Lombok Island

Abstract the availability of water resources is increasingly limited and even tends to be increasingly scarce; an in-depth study of geological-hydrogeological analysis of springs and groundwater is needed to support various community activities. This research was conducted to determine the hydrogeological system in the Pandanduri Dam area and its surroundings. Geological conditions and geomorphology determine the hydrogeological system and groundwater flow direction patterns. Geological conditions were obtained by conducting field investigations, and groundwater level data was obtained by measuring dug wells from 36 points and measuring 13 points of spring locations. Volcanic sedimentary rocks and volcanic breccia dominate the study area. Three (3) rock units can be distinguished, namely (1) the Andesite tuff breccia – pumice unit is located in the southern part of the study area, precisely in the reservoir area, and (2) the Andesite tuff breccia unit dominates located in the southern part of the study area. The study area’s eastern, western, and northern parts and (3) alluvial deposit units located in the study area covered the andesite volcanic breccia. The aquifer consists of volcanic sedimentary rock and volcanic breccia with a sandy bottom. The 2D interpretation of the dam area shows that the sandy volcanic breccia unit has a resistivity value between 5 ohms - 25 ohms in the form of lapilli tuff sand interspersed with fine tuff, located at a depth of 8 meters below the surface. The pattern of the direction of groundwater flow indicates that the movement of groundwater follows the shape of the topography that flows from the hilly area west-northwest of Santong Village to the southeastern river valley of Pandanduri Village; geological and geomorphological conditions affect this groundwater flow pattern.

Volcanic-controlled basin architecture variation and dynamic sediment filling in the South Lufeng Sag, South China Sea

Volcanic-controlled changes of basin architectures and sediments have given rise to diverse and rapidly evolving “dynamic geomorphology,” which poses challenges to successful petroleum development. Nonetheless, the accompanying volcanic deposits and landforms often produce rich and distinct seismic responses within conventional sedimentary layers, offering vital support in addressing this critical issue. Based on this, we compared the volcanic activity stages, evolution of geomorphology, and sediment dispersal processes to determine the process of basinal evolution by analyzing the episodes and distribution of volcanic-related deposits, sub-stages, seismic facies, and attributes of deposits of the South Lufeng Sag in the Pearl River Mouth Basin, South China Sea. The widespread development of strong amplitude attributes and chaotic reflection variance cube attribute spatial perspectives reveal the evolution of both intrusive and effusive facies in the lower Wenchang Formation across three stages of volcanic activity. The seismic amplitude difference of the andesite and andesitic tuff unveils the transition of the depositional pathway from north to south in the west depression with change of depocenters, lays the foundation for the dynamic geomorphic evolution of the “transitional basin” in the region. In the middle Huizhou-Lufeng uplift, the chaotic reflection with weak amplitude and obvious diapir structures revealed by andesite constrain the distribution of sedimentary space and the transformation of sedimentary pathways within the basin, and the evolution process of the “restricted basin” is summarised in terms of sedimentary filling processes. The seismic amplitude differences of basalt and andesitic tuff - related sediments in the east depression record the process of transformation from a single sedimentary channel to multi-pathway transport, which is summarised as the evolutionary model of the “diffusive basin”. This study offers a meticulous exploration into the evolutionary trajectory of dynamic geomorphology and sedimentary accumulation in a basin regulated by volcanic activity. The findings pave the way for the extensive application of this methodology in petroleum development across various geographic regions.

LATE CAMBRIAN (~490 MA) ARC VOLCANIC ROCKS OF THE NORTH TIANSHAN OF KYRGYZSTAN: AGE CONSTRAINTS FROM U–Pb ZIRCON DATING

In the present contribution, we aim to determine the age of the oldest arc-related volcanic units in the North Tianshan of Kyrgyzstan (NTS) to better understand the early evolution of subduction systems in the western part of the Central Asian Orogenic Belt. We conducted zircon U–Pb dating (LA–ICP–MS) on andesitic tuffs from the Sultansary and Tashtambektor formations, which were previously believed to be of early Cambrian and middle Cambrian to early Ordovician age, respectively. Our results reveal age estimates of 491 ± 3 and 487 ± 3 Ma for these formations, indicating that both units are late Cambrian in age. The volcanic rocks belong to a major magmatic arc with a heterogeneous basement that evolved in the NTS during the late Cambrian and early Ordovician.

Volcanic Age and Geochemistry of the Permian Linxi Formation in Northeast China: Implications for the Tectonic Evolution of the Paleo-Asian Ocean

Abstract The tectonic evolution of the Paleo-Asian Ocean (PAO) has been well studied, including its gradual narrowing and closure by subduction. However, aspects of the tectonic evolution of the oceanic domain remain unclear, including the exact timing and nature of the closure. The Central Asian Orogenic Belt (CAOB) was formed by the closure of the PAO and, therefore, contains information about the tectonic evolution of the oceanic domain. Here, we report a study of the petrology, geochronology, and geochemistry of the Taohaiyingzi section of the Permian Linxi Formation in Alukhorqin Banner (Northeast China) in the central part of the CAOB. A newly discovered andesitic tuff from the lower part of the Linxi Formation yields a weighted mean 206Pb/238U age of 262.2 ± 1.1 Ma (n = 87), indicating that the lower part of the Linxi Formation of the Taohaiyingzi section was deposited during the late Guadalupian. Provenance weathering indicators show that the sedimentary rocks of the Linxi Formation are of low maturity. Element geochemical characteristics indicate that the Linxi Formation clastic rocks were derived from eroded magmatic rocks that formed in a continental arc setting and were deposited close to the arc in a continental arc basin environment. The active margin setting was generated by the subduction of the paleo-Asian oceanic plate beneath the Xilinhot–Songliao block. The inferred palaeosalinity of the sedimentary environment changed gradually from brackish to fresh water, suggesting the end of oceanic plate subduction during the late Guadalupian, and the closure of the PAO during or after the Lopingian.

Microbially-induced K enrichments in hydrothermally altered andesitic tuffs

Microbially-induced K enrichments in hydrothermally altered andesitic tuffs

A first attempt at a provenance study in the Jadar block (Serbia) by means of U-Pb zircon geochronology

U-Pb geochronology of zircon grains retrieved from magmatic rocks intruding the Jadar block terrane in the central Balkans is used here to add new constraints on the terrane accretion processes and the provenance of crustal sources of this potentially exotic crustal block. Using an unorthodox approach, we analyzed zircons extracted from the products of Cenozoic (Cer and Boranja granitoid massifs) and Triassic magmatism (Bobija andesitic tuff - Pietra Verde). In fourteen samples of granites and epiclastites, we analyzed about 600 grains, and of these, about 30-40% were derived from the basement and were used further for the geological interpretation. Most samples show a similar Precambrian and Paleozoic age spectrum, including ubiquitous Neoproterozoic and well-defined Silurian-Ordovician populations. Only a few older zircons are present, composing minor populations at c. 1.2 Ga and 3.2 Ga. The younger zircons represent a ubiquitous Triassic population that is the strongest in all samples. This age population is most likely associated with local Permo-Triassic magmatism generated due to the opening of the Neotethys. In contrast to the magmatic rocks of Boranja and Bobija, the zircon age spectrum of the Cer polyphase pluton shows a strong Carboniferous peak, indicating a potentially important link to the Variscan margin of Eurasia. This supports opposing interpretations that either this part of the Jadar block terrane represents a southern continuation of the ?Bukkium? and Sana-Una terranes comprising displaced fragments of the southern European Variscan foreland, or, more likely, that it has an Adria affinity and that these zircons are derived from Cretaceous sediments of the Sava Zone, i.e., the suture that separates European and Adriatic domains, which were assimilated during the intrusion of the Cer granitic magmas.

Neoproterozoic storm deposits in western Yangtze: Implications for the sea conditions during the middle Sturtian glaciation

The Neoproterozoic snowball Earth hypothesis emerged to explain an inferred planetary wide extreme climate change. However, storm deposits requiring open water conditions in the Huangdongzigou Formation, South China, contradict interpretations of a global Cryogenian hard snowball Earth. These deposits accumulated during the middle Sturtian interval (690–675 Ma) on the basis of U-Pb zircon age data from andesitic tuff and coarse siltstones within the formation. Siltstones and mudstones with abundant storm-generated erosional and sedimentary structures, such as hummocky and swaley cross-stratification occur through the sedimentary succession, which require the action of oscillating ice-free water flow. Chemical weathering indices and resultant mean annual temperature calculations indicate a warm-humid environment during storm events, with the transition to a cold water depositional environment towards the top of the formation, which is possibly related to the next glacial episode.

Late Carboniferous closure of the Junggar-Balkhash Ocean: Insights from the early Permian post-accretionary magmatism in the Barleik Mountains of West Junggar, NW China

Early Permian magmatic rocks in the West Junggar Terrane (WJT, NW China) contain crucial information about the final closure of the Junggar-Balkhash Ocean (JBO) in the southwestern Altaids, whereas their tectonic settings are inconclusive. In this study, we conduct an integrated study incorporating the geochronology, geochemistry and zircon Hf isotopes of a set of volcanic and intrusive rocks from the northwestern Barleik Mountains in the central WJT. Zircon UPb ages of eight volcanic and felsic–intermediate intrusive samples are ∼292–281Ma, corresponding to a regional magmatic flare-up in the central WJT. The volcanic samples include rhyolitic tuff, andesitic tuff, and rhyolitic andesite, characterized by high-K calc-alkaline to shoshonitic I-type granite features. They yield positive εHf(t) values with a narrow range of 9.40–13.52 and two-stage model ages from 421 Ma to 672 Ma. Above isotopic features, in combination with their relatively low Mg# values of 25–35, demonstrate that they were generated by partial melting of the juvenile lower crust. Felsic intrusive rocks include peraluminous I-type granitic porphyry and A2-type K-feldspar granite, and their low Mg# values (21–35) and trace element ratios suggest the partial melting from lower crustal rocks. By contrast, intermediate intrusive rocks include monzonite, diorite and a dioritic dyke, which represent fractionated partial melts sourced from the underplated depleted mantle-derived magma. Based on the occurrence of I-type and A2-type rocks, together with the coeval extensional strike-slip fault systems and a late Carboniferous angular unconformity, we infer that the early Permian magmatism in the central WJT resulted from an extensional post-accretionary setting. Taken together with similar geological evidence from the WJT and East Kazakhstan, the final closure of the JBO is suggested to occur in the late Carboniferous.

Genesis of the Kiruna-type Nixintage iron deposit, Chinese Western Tianshan, NW China: Constrains of ore geology, geochemistry and geochronology

The Nixintage iron deposit is located in the central segment of the Awulale metallogenic belt, Chinese Western Tianshan. Iron ores are mainly hosted by andesitic tuff and andesite of the Carboniferous Dahalajunshan Formation. The paragenetic sequence includes a magmatic magnetite-apatite stage (I); a magmatic–hydrothermal stage (II), and three substages can be divided, including magnetite-albite substage (II-1), magnetite-chlorite-pyrite substage (II-2), magnetite-quartz-calcite substage (II-3); and a late hydrothermal quartz-calcite-sulfides stage (III). Anhedral, fine-grained magnetite associated with apatite in brecciated and matrix ores formed in stage I with relatively variable compositions, most probably indicate the fast crystallization under a disequilibrium condition. The high-grade magnetite orebodies mainly formed in the stage II, are featured by widespread hydrothermal mineral assemblages associated with the ores. Magnetite formed in this stage has medium-to-high concentrations of V, low-to-medium concentrations of Ti, Cr, relative depletion of Mg, Ni, K, and these data mainly plot in the Kiruna and porphyry fields of discriminant diagrams that comparable to magnetite from typical Kiruna-type iron deposits. Both stages I and II magnetites show similar wide δ18O ranges and with peak values at 6.0–10.0 ‰, heavier than typical Kiruna-type deposits, while could be attributed to the relatively low crystallization temperature inferred by microthermometric data of a previous study. The δ34S values of pyrite formed in different stages range between 0.1 and 2.4 ‰, comparable to the sulfur isotopic composition of the mantle-derived magma. These features indicate that stage I iron mineralization was generated by the extrusion of iron phosphorous oxide melts separated from the parental silicate magma. Subsequent deuteric fluids exsolved from basaltic to andesitic melts during the late stage of volcanism, generated magmatic–hydrothermal iron mineralization in stage II, and the continuous evolution of the deuteric fluids formed stage III hydrothermal veins. In summary, integrated evidence suggests the Nixintage is a Kiruna-type iron deposit.Zircon U-Pb ages of ore-hosting andesite and andesitic tuff are 317.6–314.4 Ma, and timing for iron mineralization was inferred at the same time, i.e., ca. 315 Ma. Previously published petro-geochemical data combined with our geochronological data of these rocks, suggest the ore-related volcanism in Nixintage probably originated from the partial melting of the mantle wedge modified by subducted fluids under a Late Carboniferous continental arc setting. Consequently, a genetic model for the studied deposit could be created. Furthermore, the southeast of the Nixintage nearer to the vent might have potential for prospecting large Kiruna-type iron deposits.

Provenance Tracing and Age Analysis of Lead–Zinc Mineralization in Qiyimuchang, Inner Mongolia, NE China

The Qiyimuchang lead–zinc deposit is an important deposit in the Erguna Massif on the west slope of Daxinganling, for which the material source and age of mineralization remain unclear. The lead–zinc deposit in Qiyimuchang has been observed to occur in Jurassic volcanic strata as a vein-like orebody, and its strike is nearly perpendicular to that of the strata and the regional structures of the orogenic belt. The ore is mainly composed of sphalerite, galena, chalcopyrite, pyrite, and quartz, and hydrothermal alteration zones dominated by silicification, fluoritization, and pyritization are common within 1–5 m on both sides of the vein. The metasomatic lead–zinc mineralization is characterized by a massive vein structure. The mineralization process can be divided into three stages, pre-ore (mainly quartz, arsenopyrite and a small amount of pyrite), ore-formation (pyrite, chalcopyrite, sphalerite, galena, fluorite, and a small amount of tetrahedrite), and post-ore (quartz-calcite veinlets with a small amount of pyrite). Element and isotope geochemical studies show that the trace element compositions of the wall rocks (andesite, tuff, etc.) of Jurassic volcanic rocks in the ore bodies and surrounding rocks reflect affinity or similarity between them. The S isotopic composition of sulfide minerals in the metallogenic stage (δ 34SV-CDT = 1.6‰~4.8‰) indicate the sulfur isotopic composition of the magma. The Pb isotopic compositions of sulfide minerals (38.5–38.39, 15.55–15.62, and 18.33–18.41 for 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb, respectively) in the metallogenic stage are relatively concentrated and close to the average Pb isotopic compositions of the mantle and average Pb isotopic composition of an orogenic belt, indicating that the ore-forming metals are likely to be a mixed source of crust and mantle. A new zircon U-Pb age of 150.8 ± 1.3 Ma (MSWD = 0.74) was obtained from andesitic tuff. Collectively considering the regional geology and ore deposit geological analysis, the lead–zinc mineralization in Qiyimuchang possibly occurred during the early Cretaceous. The ore-forming processes belong to Cretaceous magmatic-hydrothermal activity in extensional tectonic setting.

Lithospheric dripping in a soft collision zone: Insights from late Paleozoic magmatism suites of the eastern Central Asian Orogenic Belt

The closure of Paleo-Asian Ocean is considered to have occurred along the Solonker Suture in the southernmost segment of the Central Asian Orogenic Belt (CAOB), the largest Phanerozoic accretionary orogen on the globe. The suture branches to the east to form the northern Hegenshan–Heihe Suture and the southern Solonker–Changchun Suture. The Hegenshan–Heihe Suture is an ideal natural laboratory for studying the post-collisional geodynamic processes operating in a soft collision zone driven by divergent double-sided subduction. Here we report results from an integrated study of the petrology, geochronology, geochemistry, and Sr–Nd–Hf isotopic compositions of the Early Carboniferous–Early Permian magmatic suite in the Hailar Basin of the Xing’an–Erguna Block. The Early Carboniferous igneous rocks are represented by 356–349 Ma andesitic tuffs, exhibiting typical subduction-related features, such as enrichment in large-ion lithophile elements and depletion in high-field-strength elements. These features, together with the relatively depleted Sr–Nd–Hf isotopic compositions, constant Nb/Y values, but highly variable Rb/Y and Ba values indicate that these rocks were generated by partial melting of a depleted mantle wedge metasomatized by slab-derived fluids. The Late Carboniferous–Early Permian magmatic suite (317–295 Ma) is characterized by high Sr contents (313–1080 ppm) and low Y contents (5–13 ppm), and these can be subdivided into calc-alkaline adakitic rocks and high-K calc-alkaline adakitic rocks. The calc-alkaline adakitic rocks have higher values of Sr/Y, (Sm/Yb)source normalized, and Mg#, and lower values of Y, Ybsource normalized, and K2O/Na2O than the high-K calc-alkaline adakitic rocks, which suggests that the former was generated by partial melting of foundered lower continental crust and the latter by partial melting of normal lower continental crust. Based on our new data, in conjunction with those in previous studies, we conclude that the tectonic evolution of the Hegenshan–Heihe Suture involved Early Carboniferous double-sided subduction of the Nenjiang Ocean, latest Early Carboniferous soft collision between the Xing’an–Erguna and Songliao blocks, and Late Carboniferous–Early Permian post-collisional extension. We also propose a new geodynamic scenario in which removal of the lithospheric root might have occurred in a soft collision zone during the post-collision period via repeated and localized lithospheric dripping, which results from combinedeffects of hydration weakening of the lithosphere caused by pre-collision subduction and asthenospheric stirring triggered by slab break-off.

Characteristics and Main Controls of Tectonic Fractures and Their Contribution to Deep Tight Reservoirs: A Case Study of the Huoshiling-Shahezi Formations in Gudian Half-Graben, Songliao Basin, China

AbstractThe deep volcanic and clastic rocks in the Songliao Basin are typical tight reservoirs with ultralow porosity and permeability. Natural fracture determines the effective reservoirs in the deep strata. Integrated core and thin section observations, image logging, physical property measurement, X-ray diffraction, and seismic attribute analysis were applied to ascertain the characteristics and genetic mechanisms of the tectonic fractures in the Huoshiling-Shahezi Formations of the Gudian half-graben. The contribution of the fractures to deep tight reservoirs was also discussed. Results showed that tectonic fractures are mainly tension, shear, and slip fractures. The density of the fractures in andesitic tuffs with high clay minerals content is significantly higher than that in the other rock types. The main controls of the developmental degree of fractures are tectonism. Three sets of fractures were identified based on the genetic connection between fracture formation and tectonic stress. The NNW-trending tension fractures were formed in the syn-rift stage and successively extended in the post-rift stage. The regional compressional stress drove the formation of the NEE-trending shear fractures and NNW-trending “X” plane-conjugated shear fractures in the postextrusion stage. The averaged porosity and permeability of the reservoirs are generally less than 6.0% and lower than 0.06 mD. The pores can hardly independently provide migration pathways and storage spaces, but the fractures significantly improved the reservoir properties. The fractures were well developed in the regions near the Gudian fault, fault transfer zones, and volcanoes, indicating the distribution of potential reservoirs. Moreover, unraveling the types and orientations of the fractures will provide an essential basis for the analysis of hydrocarbon migration and hydraulic fracture treatments.

Timing and causes of forest fire at the K–Pg boundary

We report K–Pg-age deposits in Baja California, Mexico, consisting of terrestrial and shallow-marine materials re-sedimented onto the continental slope, including corals, gastropods, bivalves, shocked quartz grains, an andesitic tuff with a SHRIMP U–Pb age (66.12 ± 0.65 Ma) indistinguishable from that of the K–Pg boundary, and charred tree trunks. The overlying mudstones show an iridium anomaly and fungal and fern spores spikes. We interpret these heterogeneous deposits as a direct result of the Chicxulub impact and a mega-tsunami in response to seismically-induced landsliding. The tsunami backwash carried the megaflora offshore in high-density flows, remobilizing shallow-marine fauna and sediment en route. Charring of the trees at temperatures up to > 1000 °C took place in the interval between impact and arrival of the tsunami, which on the basis of seismic velocities and historic analogues amounted to only tens of minutes at most. This constrains the timing and causes of fires and the minimum distance from the impact site over which fires may be ignited.

Provenance and Tectonic Setting of the Middle Permian Zhesi Formation in Eastern Inner Mongolia, China: Implications from Petrology, Mineralogy, and Element Geochemistry

Four sets of high-quality source rocks are found in the Permian Zhesi Formation in eastern Inner Mongolia, China, which has good oil and gas resource potential. However, the research on the provenance and source area characteristics of the sediments is relatively weak. Petrographic, mineralogical, and geochemical analyses were conducted on mudstones and siltstones and fine sandstones from the eastern Inner Mongolia to investigate the provenance of the sediments, as well as the weathering intensity and tectonic setting of the source region. Petrographic data indicate that average quartz–feldspar–lithic (Q–F–L) proportions in the sandstones are Q = 43%, F = 3%, and L = 54%; the lithic fraction mainly contains volcanic clasts. The chemical index of alteration in mudstones varies from 73 to 80 (average 76), while the index of chemical variability ranges from 0.39 to 0.79 (average 0.75), and the average Th/U ratio is 3.66. Chondrite-normalized rare-earth element (REE) distributions show light REEs that are enriched relative to heavy REEs and a prominent negative Eu anomaly. These data indicate that the sediments are compositionally immature and have a weak-medium degree of weathering in the source region. The petrographic and mineralogical characteristics, combined with Zr/Sc–Th/Sc, Hf–La/Th, and Co/Th–La/Sc discrimination diagrams, reveal that these sediments are mainly derived from the rhyolite, basaltic andesite, and andesitic tuff in the early Permian Dashizhai Formation. Multidimensional tectonic discrimination diagrams, including geochemical data and Dickinson triangular charts, indicate that the tectonic setting of the provenance area is a continental island arc related to the active continental margin. These conclusions further confirm tectonic and magmatic events of the early Permian in eastern Inner Mongolia, China.

Mineral paragenesis and stratigraphic setting of the Neoproterozoic volcano-sedimentary succession of Samran Group, Jabal Farasan Area, West central Arabian Shield, Saudi Arabia

Jabal Farasan is located in the west central part of the Arabian Shield. The present study aims to reveal the stratigraphic setting and mineral paragenesis of the exposed volcano-sedimentary succession of the Samran Group in Jabal Farasan area. The succession of Samran Group is composed of three successive facies: the lower interbedded andesitic tuffs and tuffaceous andesites and trachyte’s (F1), the middle-altered quartz diorite/andesite (F2) and, an upper interbedded andesitic tuff, tuffaceous andesites and trachytes (F3). The vertical variations in the petrographic lithotypes depend mainly on the position of the depositional sites relative to the volcanic centers (proximal and distal). Both the volcanic rocks and the associated units are subjected to syn-and post-depositional diagenetic/metamorphic processes. These processes include the formation of the Fe2+-silicates: (i.e., chlorite instead of the volcanic ashes and the formation of plagioclase minerals). Post diagenetic recrystallization of the tuffaceous mudstones and the formation of microcrystalline quartz. The diagenetic oxidation of the Fe2+-silicates led to the formation of volcaniclastic red beds in certain stratigraphic horizons.

Petrography And Field Study Of Andesitic Ignimbrite In Temangan, Kelantan

The volcanic rocks in Temangan, Kelantan consist of felsic to intermediate volcanic rocks, that is mainly of pyroclastic with rhyolitic, dacitic, and andesitic tuff. A geological review has been carried out in Kampung Bukit Besi, Temangan, in Kelantan, Malaysia, which is composed of schist, shale, andesite, and ignimbrite. In Temangan, andesite and ignimbrite show an intimate relationship, as the ignimbrite exists as the fragments and andesite as the matrix. The methodology used in this study are petrography and X-ray Diffraction (XRD) analyses, to determine the mineralogical composition of andesitic ignimbrite. Andesite shows aphenitic and porphyritic textures and consist of pyroxene, plagioclase, alkali feldspar, quartz, biotite and iron oxides. A range of plagioclase textures indicate imperfect equilibrium condition from andesite, reflecting plagioclase dissolution and regrowth. The structural analysis suggest that thrust fault occurred in the study area. Andesite and ignimbrite of the two stages are suggested to have derived from the andesite magma eruption which produced pyroclastic flow eruptions in small amount in most caldera volcanoes at high temperature gradient.

Zircon U–Pb geochronology, Hf isotope composition, and petrochemical characteristics of Paleocene granitoids in the western Gangdese Belt, Tibet

Abstract —The research team studied the petrology, whole-rock geochemistry, zircon U–Pb age, and stable isotopic characteristics of the Rongguo Longba and Garongcuo granites of the Nuocang area to understand better the impact of Neo-Tethys ocean subduction and In-dia–Eurasia continental collision on Paleocene tectonomagmatic processes along the southern margin of the Gangdese Belt. The Rongguo Longba granite and Garongcuo granite porphyry formed at 61.86 and 62.17 Ma, respectively. The Nuocang granitoids are characterized by (1) high SiO2, NaO2, and Al2O3 contents and low FeOtot, MgO, and TiO2 contents; (2) LREE and LILE enrichment and HREE and HFSE (Nb, P, and Ti) depletion; and (3) obvious negative Eu anomalies. These features indicate that the Nuocang granites are of the high-K calc-alkaline and peraluminous granite types. Furthermore, their zircon Hf isotope characteristics suggest that the magma source region has an ancient crystalline basement. The basaltic andesitic crystal tuff is the product of garnet–peridotite partial melting and crust contamination from rising magma emplacement.

Geology, Rock Geochemistry and Ore Fluid Characteristics of the Brambang Copper-Gold Porphyry Prospect, Lombok Island, Indonesia.

Brambang is one of the porphyry copper-gold prospects/deposits situated along eastern Sunda arc. This study is aimed to understand geological framework, alteration geochemistry and ore fluid characteristics of the prospect. Fieldworks and various laboratory analyses were performed including petrography, ore microscopy, rock geochemistry, chlorite chemistry and fluid inclusion microthermometry. The prospect is composed of andesitic tuff and diorite which are intruded by tonalite porphyries. Tonalite porphyries are interpreted as ore mineralisation-bearing intrusion. Various hydrothermal alterations are identified including potassic, phyllic, propylitic, advanced argillic and argillic types. Ore mineralisation is characterized by magnetite and copper sulfides such as bornite and chalcopyrite. Potassic alteration is typified by secondary biotite, and associated with ore mineralisation. Mass balance calculation indicates SiO2, Fe2O3, K2O, Cu and Au are added during potassic alteration process. Ore forming fluid is dominated by magmatic fluid at high temperature (450-600ºC) and high salinity (60-70 wt. % NaCl eq.). Hydrothermal fluid was diluted by meteoric water incursion at low-moderate temperature of 150-400ºC and salinity of 0.5-7 wt. % NaCl eq.

Ore genesis and tectonic setting of the Bieluwutu Cu-Pb-Zn volcanogenic massive sulfide deposit in Xing’an-Mongolia orogenic belt, China

The Bieluwutu Cu-Pb-Zn deposit is located in the Ondor Sum region of the western Xing’an-Mongolia orogenic belt, North China. The host rocks of the deposit consist of metasandstone, tuffaceous slate, andesitic tuff and fragmented felsic volcanic rocks, which have previously been regarded as the Early Carboniferous Amushan Group. Zircon U-Pb ages for two tuffaceous units are 435 ± 2 Ma and 430 ± 2 Ma, showing that volcanism occurred in the Early Silurian. The tuffaceous rocks are enriched in large ion lithophile elements (LILE; e.g., Rb, Ba, K) and light REE, and depleted in high field strength elements (HFSE; e.g., Nb, Ta and Ti) with depleted isotopic components (εNd(t) = 0.14–0.84), indicating that they were derived from partial melting of lower continental crust with the involvement of mafic magma.Bieluwutu is intended to be a Kuroko-type VHMS deposit formed in an interarc rift basin in the Early Silurian. Three types of ores have been identified at Bieluwutu, including massive Pb-Zn, brecciated Cu-Zn and disseminated Cu ores. Results of sulfide laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Se and Sn are enriched in chalcopyrite from the disseminated and brecciated ores with high Se/Te ratios. Tellurium, Co, Pb and Bi are enriched in chalcopyrite, sphalerite and pyrite from the brecciated ores, whereas Mn, Ni and Tl concentrations are higher in pyrite from the massive ores. These differences suggest a decreasing temperature and increasing f(O2) trend from the disseminated to brecciated and massive ores. High contents of Mn, Tl, Ni in massive ores are typical for metals derived from surrounding felsic volcanic rocks. Strong enrichment of trace elements, such as Bi, Te, Se and Sn, is consistent with a magmatic contribution to the ore-forming fluids. The underlying subvolcanic intrusion not only served as a heat engine but also supplied volatiles and metals.