Porphyritic Andesite Research Articles

A special source: making porphyritic andesite axeheads at the Eagle’s Nest, Lambay, Ireland in the Early Neolithic

ABSTRACT This paper considers the Early Neolithic phase of activity on an axehead quarry at the Eagle’s Nest, Lambay, a small island off the east coast of Ireland. The site is best known for activity in the later Neolithic and its cultural connections with the developed passage tomb tradition. One area of the site has produced evidence for quarrying from the thirty-eighth or thirty-seventh century cal BC, supplying secure evidence that axe production was integral to the Neolithic material world in Ireland from the beginnings of this period. Porphyritic andesite would seem a counter-intuitive choice to make stone axeheads, its naturally occurring internal fissuring resulting in a high likelihood of failure during working. On the other hand, when ground and polished it has a very distinctive visual appearance and texture with a lustrous quality. This paper examines the ontological significance of this transformation from source to special objects.

Metasomatic enrichment of the sub-arc mantle: Evidence from the petrography and geochemistry of the xenolith-bearing andesites from Dinem Island, Batanes, Philippines

The Babuyan Segment of the Luzon Arc in the Philippines is divided into an older west volcanic chain (WVC) and a younger east volcanic chain (EVC) based on the geochemical and geochronological characteristics of their volcanic rocks. Mantle and crustal xenoliths have been previously reported in the volcanic rocks of young Batan (EVC) and Sabtang (WVC). In this work, we present new petrographic and geochemical data on volcanic rocks from Dinem Island (EVC), which also host mantle and crustal xenoliths. These volcanic rock data are compared to the data of other volcanic centers in the region to better understand magmatic-metasomatic processes that occur beneath island arcs.The Dinem volcanic rocks are generally porphyritic andesites, with plagioclase and hornblende phenocrysts, minor clinopyroxene and Fe-Ti oxides. Correlation between major oxides (i.e., K2O, Na2O, TiO2, CaO and Al2O3) and trace elements (i.e., Ni and Cr) with FeO*/MgO suggests that the Dinem volcanic rocks are related by magmatic differentiation. These rocks also record enrichment in large ion lithophile elements (e.g. Rb, Ba, Th) and depletion in high field strength elements (e.g. Nb, Ta, Ti), which are typical of arc volcanic rocks. The volcanic rocks from Dinem also have elevated (La/Sm)N and Th/Yb and low Ba/Th values relative to WVC volcanic rocks. These trace element ratios and enriched LREE signature suggest that the Dinem and younger Batan volcanic rocks of the EVC were derived from a mantle wedge that is highly metasomatized by slab-derived fluids/melts relative to the source region of the WVC volcanic rocks.

Water Sowing and harvesting application for water management on the slopes of a volcano

The present study aims to elaborate a hydrogeological characterisation in the Water Sowing and Harvesting context. The study is focused on rural parishes in the Ecuadorian Andes that, despite their proximity to snow sources (Chimborazo glaciers), need more supply of this resource, to satisfy the demand of a population of 70,466 inhabitants. The study is based on hydrology and geomorphological analysis, a geophysical exploration, and a definition of water management strategies. The application of non-destructive geophysical methods and Geographic Information Systems support the hydrogeological study and the proposal of strategies for sustainable water management on the slopes of the Chimborazo volcano. An aquifer potential was identified (sand, gravel and fractured porphyritic andesites) with resistivity values between 51.3 and 157 Ω m at an approximate depth of 30 m from the geophysical characterisation addressed. This potential saturated zone is on the southern slope of the Chimborazo volcano within the hydrographic watershed, with favourable drainage networks for water accumulation. The aquifer shows a high-water saturation level but uncontrolled losses. As a consequence of these characteristics, alternatives for managing water resources are proposed, such as wells construction, using Water Sowing and Harvesting system methods (“camellones”) based on Nature-Based Solutions, dam construction and environmental education. The different proposals are associated with the four sustainability axes of Brundtland (economic, social, environmental and cultural axis) and contribute to the sixth objective of the Sustainable Development Goal 2030 Agenda.

The magmatism of Atienza (NW Iberian Chain, Spain): age, origin and architecture of the magmatic plumbing system

A sill covering an area of more than 15 km2, several dykes up to 5 m thick and a volcanoclastic deposit crop out with similar petrology in the sector of Atienza (NW Iberian Chain, Spain). They consist of calc-alkaline porphyritic andesites with phenocrysts of plagioclase, amphibole, biotite, garnet and orthopyroxene. Based on U–Pb zircon analysis, an age of 290 ± 3 Ma (Sakmarian-Artinskian in the Cisuralian) has been calculated for this magmatism. The chemistry and geothermobarometry on amphibole crystals revealed crystallisation at different depths between 31 and 16 km, involving several events of magma recharge and fractional crystallisation. Magma ascent led to destabilisation of the amphibole crystals, their replacement by biotite, and the formation of thick microcrystalline coronas. Whole-rock trace element and isotopic compositions support a strong crustal influence in the origin of the magma. Crustal melting was produced by heating generated after lithospheric thinning, delamination, and asthenospheric rise produced after the uplift of the Variscan Orogen and the oroclinal folding of the Iberian Massif.

Characteristics of the gold-bearing and barren quartz veins at the Zaylik-Sarilar epithermal deposit, Ahar-Arasbaran Zone, NW Iran: Evidence from mineralogy, alteration, texture and fluid inclusion

The Zaylik-Sarilar epithermal deposit is located 35 km southeast of Ahar in the Ahar-Arasbaran Zone in the Alborz-Azerbaijan Magmatic Belt, NW Iran. Exposed rocks in the Zaylik-Sarilar deposit are mainly composed of Eocene volcanic rocks and Miocene dacite-rhyodacite that are intruded by younger intrusions. The deposit occurs within a sequence of Eocene porphyritic andesite and andesitic lithic tuff. Mineralization occurs as open space filling, taking place as irregular veins, veinlets, and hydrothermal breccias. The mineralization zones can be categorized into two main groups according to sulfides and sulfosalts mineralogy, alteration assemblages, ore textures, and fluid inclusion data. The first group consists of gold-bearing quartz-sulfide ± breccia veins, silicified-phyllic ± argillic zones, and a few quartz-calcite veins. The second group is composed of barren milky (or white) quartz veins, silicified lithocaps, and argillic-kaolinite ± silicic zones. Pyrite, chalcopyrite, bornite, galena, sphalerite, and Au-Ag sulfosalts were identified in ore paragenesis of the gold-bearing veins. Pyrite is the main sulfide mineral in the barren quartz veins and silicified lithocaps. Gold and silver were enriched during oxidation and supergene alteration of the gold-bearing veins. Textural evidences from the gold-bearing veins, such as mosaic breccia monomicts, floating clast breccias, hydrothermal breccias, colloform-crustiform textures, ginguro bands, dendrite textures, and rarely lattice- and parallel-bladed calcite replacement textures, suggest that boiling occurred in the veins. Comb, cockade, reed molds, zonal, and feathery textures are common in the barren veins and silicified lithocaps. Fluid inclusion data show a decreasing trend in salinity and homogenization temperature (Th) from the gold-bearing quartz veins to the barren ones. The average salinity and homogenization temperature (Th) of fluid inclusions from the gold-bearing veins are 1.05 wt% NaCl equiv. and 297 °C, respectively; higher than the average salinity (0.68 wt% NaCl equiv.) and homogenization temperature (192 °C) of fluid inclusions from the barren quartz veins. Th versus salinity diagram suggests that boiling was the main mechanism of ore deposition in the gold-bearing quartz veins and silicified zones. These data propose that the barren quartz veins and silicified lithocaps were formed by cooling. A combination of the geologic, mineralogic, alteration, and fluid inclusion data from the Zaylik-Sarilar deposit represents an epithermal system of low-sulfidation type. Structurally, mineralization has been controlled through the NW-trending strike-slip principal displacement zone and it’s subsidiary Riedel fractures in response to a N-trending compression in the Arabia-Eurasia collision zone.

Damage amplification during repetitive seismic waves in mechanically loaded rocks

Cycles of stress build-up and release are inherent to tectonically active planets. Such stress oscillations impart strain and damage, prompting mechanically loaded rocks and materials to fail. Here, we investigate, under uniaxial conditions, damage accumulation and weakening caused by time-dependent creep (at 60, 65, and 70% of the rocks’ expected failure stress) and repeating stress oscillations (of ± 2.5, 5.0 or 7.5% of the creep load), simulating earthquakes at a shaking frequency of ~ 1.3 Hz in volcanic rocks. The results show that stress oscillations impart more damage than constant loads, occasionally prompting sample failure. The magnitudes of the creep stresses and stress oscillations correlate with the mechanical responses of our porphyritic andesites, implicating progressive microcracking as the cause of permanent inelastic strain. Microstructural investigation reveals longer fractures and higher fracture density in the post-experimental rock. We deconvolve the inelastic strain signal caused by creep deformation to quantify the amount of damage imparted by each individual oscillation event, showing that the magnitude of strain is generally largest with the first few oscillations; in instances where pre-existing damage and/or the oscillations’ amplitude favour the coalescence of micro-cracks towards system scale failure, the strain signal recorded shows a sharp increase as the number of oscillations increases, regardless of the creep condition. We conclude that repetitive stress oscillations during earthquakes can amplify the amount of damage in otherwise mechanically loaded materials, thus accentuating their weakening, a process that may affect natural or engineered structures. We specifically discuss volcanic scenarios without wholesale failure, where stress oscillations may generate damage, which could, for example, alter pore fluid pathways, modify stress distribution and affect future vulnerability to rupture and associated hazards.

Andesitic flow rheology of Mount Popa volcano, Myanmar

Mount Popa is a conspicuous dormant volcano, which lies on the volcanic island arc (NS-trending central volcanic line) through the Central Myanmar Basin tectonically. The rheology of lava flows is determined by the phenocryst distribution in the andesitic rocks of Mount Popa, Myanmar. Particularly, the andesitic rock units are differentiated as V1-flow andesite, Nagale-Legyingon plateau andesite, Popa plateau andesite, V3-flow andesite, and V4-flow andesite. The different flow units are megascopic ally very similar in color and texture to porphyritic andesite or augite andesite but different in grain size, and the amount of phenocryst. The phenocryst distribution is graphically correlated with the Newtonian and non-Newtonian flow to interpret the rheology of lava flow during the Pliocene-Holocene eruption of the Mount Popa volcano. A new method which is simplest and practiced to identify the porphyritic andesitic rocks or lava flows not only for the stratigraphy but also the rheology.

Characteristics of Engineering Geology in Talegong Road, Talegong, Garut, West Java, Indonesia

Talegong road, Garut, West Java, is provincial road with a length of 7 kilometers that connects Garut and Bandung. The road segment KM 2.3 – KM 7 is located between the steep slope of high hills and has potential for landslide. To find out the landslide potential, determining the characteristics of geology and engineering geology at this road segment are needed. The methods used in this research are engineering geology mapping (geomorphology, lithology, structural geology and rock mass quality) and laboratory analyses of soil and rock properties index, shear strength test, petrographic analysis and uniaxial compressive strength test. The results of geological mapping show the aspect geomorphological in the area consists of high hills with rather steep to very steep slopes. Lithological, the area consists of aphanitic andesite and porphyritic andesite. The area is dominated by Northeast – Southeast stress regime. In term of rock mass quality, the study area consists of three class with value in Rock Mass Rating classification, which are good rock, fair rock, poor rock and no value rock (soil). The study area is divided into three units in the engineering geological map: (1) unit A has fair – good rock (II – III) with rather steep - very steep slope with low landslide potential, (2) unit B has fair rock (III) with steep – very steep slope with medium landslide potential, and (3) unit C has poor – no value rock or soil (IV – 0) with a very steep slope with high landslide potential.

Mineralogy, Geochemistry, and Age Constraints on the Axinite-Bearing Gukjeon Pb–Zn Skarn Deposit in the Miryang Area, South Korea

The axinite-bearing Gukjeon Pb–Zn deposit is hosted by the limestone, a member of the Jeonggaksan Formation, which, in turn, forms the part of the Jusasan subgroup of the Yucheon Group in the Gyeongsang Basin in the southeastern part of the Korean Peninsula. In this study, we attempted to interpret the spatial and temporal relationships among geologic events, including the mineralization of this deposit. We constructed a new 3D orebody model and suggested a relationship between skarn alteration and related mineralization. Mineralization timing was constrained using SHRIMP zircon age dating results combined with boron geochemistry on coeval intrusive rocks. Skarn alterations are restrictively found in several horizons of the limestone formation. The major skarn minerals are garnet (grossular), pyroxene (hedenbergite), amphibole (actinolite and ferro-actinolite), axinite (tizenite and ferro-axinite), and epidote (clinozoisite and epidote). The three stages of pre-skarn, syn-skarn, and post-skarn alteration are recognized within the deposit. The syn-skarn alteration is characterized by prograde metasomatic pyroxene and garnet, and the retrograde metasomatic amphibole, axinite, and epidote. Major skarn sulfide minerals are sphalerite, chalcopyrite, galena, and pyrite, which were predominantly precipitated during the retrograde stage and formed amphibole and axinite skarns. The skarn orebodies seem to be disc- or flat-shaped with a convex form at the central part of the orebodies. The vertical ascending and horizontal infiltration of boron-rich hydrothermal fluid probably controlled the geometry of the orebodies. Considering the whole-rock major, trace, and boron geochemical and geochronological results, the timing of Pb–Zn mineralization can be tightly constrained between the emplacement of boron-poor intrusion (fine-grained granodiorite, 82.8 Ma) and boron-rich intrusion (porphyritic andesite in Beomdori andesitic rocks, 83.8 Ma) in a back-arc basin setting. The boron for mineralization was sourced from late Cretaceous (Campanian), subduction-related magmatic rocks along the margin of the Pacific plate.

Magma mixing, zircon U–Pb ages and Hf isotopes: Insights for the Miocene magmatic plumbing system in the Soroche Porphyry, Puna Argentina, Central Andes

This research highlights the importance to study the magmatic plumbing systems in Southern Puna, NW Argentina, emphasizing the significance of understanding the genesis of sub-volcanic bodies and their implications for the crustal assimilation and recycling processes. In the southeastern edge of Ratones salar, Southern Puna, there is an intrusive body cropping out, named Soroche Porphyry. This intrusion is formed by porphyritic rhyodacitic, basaltic andesites, and porphyritic andesitic rocks, with magma mixing relations between the mentioned lithologies. The main features of the Soroche Porphyry are described to interpret the dynamic aspects of magma mixing, identify and define textural, mineralogical, and geochemical features, directly related to the mentioned process. Taking into account these features, the results showed that a hybrid magma (homogeneous porphyritic andesite) was produced by mixing processes between basaltic andesitic and rhyodacitic magmas, whereas, the heterogeneous porphyritic andesite represent mingling areas, whereby the end members are easily identified. Furthermore, we dated the main rocks of the porphyry using zircon U–Pb methodology by LA-MC-ICP-MS, complemented by Hf isotopes analyses. The geochronological data evidenced magmatic activity around ~15 Ma, allowing the correlation of the Soroche Porphyry with the Inca Viejo Formation. The basaltic andesites yielded a zircon U–Pb age of 15.63 ± 0.08 Ma, the heterogeneous porphyritic andesites displayed an age of 15.52 ± 0.16 Ma, and the rhyodacites showed an age of 15.13 ± 0.12 Ma. The isotopic ƐHf (15 Ma) values from the rhyodacite between −4.9 and −11.3, suggested a great amount of crustal components, evidencing that the rhyodacitic magmas derived from assimilating and recycling crustal rocks probably from the lower Paleozoic rocks.

Lithogeochemical exploration for delineating primary gold occurrences in West Kao area, North Halmahera District, North Maluku Province

Halmahera Island retains several gold deposits. One of the gold deposits is called as low sulphidation epithermal (LSE) quartz veins which is currently being mined and is situated in the Gosowong goldfield. The veins mostly originated in N-S and NNE-SSW direction. This study is aimed to determine the prospect area in the northern portion of Gosowong goldfield covering the West Kao sub district based on surface mapping and rock/float- and BLEG stream sediment survey. A total of 16 rock/vein float and 120 BLEG samples were analyzed by FA/AAS and CNO2 cyanide leach methods, respectively. The study area is occupied by tuffaceous sandstone, andesite, porphyritic andesite and lava andesite units. In the eastern part, tuffaceous sandstone is suffered from argillic and propylitic alteration, which may be controlled by the NW-SE-trending structures. The gold grade of rock/float samples is up to 0.044 ppm. BLEG data indicates a calculated threshold of 10 ppb for Au and 72 ppb for Ag. The highest Au and Ag contents (anomalies) are identified in the eastern part of the study area. This is spatially (and maybe genetically) related to the argillic-altered tuffaceous sandstone, structures and occurrences of quartz vein floats. To follow up this finding, a detailed exploration is recommended to be conducted within the prospect area.

THE ORIGIN AND QUALITY OF THE GROUNDWATER OF THE RAWADANAU BASIN IN SERANG BANTEN, INDONESIA

Rawadanau is a tropical mountain swamp located in Serang, Banten, Indonesia. Rawadanau groundwater is the main source of supply for the Cilegon Banten industrial area. Knowing the origin and quality of the groundwater can help preserve existing resources. This paper aims to clarify the origin of Rawadanau groundwater with new evidence of stable isotopes (18O and 2H) and hydrochemical data. Field measurements included pH, temperature, EC, HCO3ˉ, while the analyses of cations, anions and stable isotopes were carried out in the laboratory. The existing water supplies include springs, excavated wells, and river water. Cluster hierarchy analysis based on water chemistry and stable isotopes can be grouped into two clusters, cluster K (K1 and K2) and cluster L. Data δ18O and δ2H springs in Rawadanau indicate that they are of meteoric origin and that there has been evaporation from several springs. Water comes from meteoric water with a stable isotope content of δ18O between -6.39 to -4.82 ‰ and δ2H between -41.35 to -31.30 ‰, which are controlled by two main mechanisms, namely rock dissolution and evaporation dominance. Aquifers are composed of volcanic rocks with a dominant composition of porphyritic andesite, basaltic andesite, and andesite. According to the multivariate statistical analyses results other than pH and SO4 2-, all parameters (cations and anions) showed a significant correlation. There are four hydrochemical facies of groundwater, namely Ca-HCO3, Ca-Mg-HCO3, Mg-Ca-HCO3, and Na-Cl.

Understanding mafic-felsic magma interactions in a subvolcanic magma chamber using rapakivi feldspar: A case study from the Bathani volcano-sedimentary sequence, eastern India

The Ghansura Rhyolite Dome of the Bathani volcano-sedimentary sequence in eastern India originated from a subvolcanic felsic magma chamber that was intruded by volatile-rich basaltic magma during its evolution leading to the formation of a porphyritic andesite. The porphyritic andesite consists of rapakivi feldspars, which are characterized by phenocrysts of alkali feldspar mantled by plagioclase rims. Results presented in this work suggest that intimate mixing of the mafic and felsic magmas produced a homogeneous hybrid magma of intermediate composition. The mixing of the hot volatile-rich mafic magma with the relatively colder felsic magma halted undercooling in the subvolcanic felsic system and produced a hybrid magma rich in volatiles. Under such conditions, selective crystals in the hybrid magma underwent textural coarsening or Ostwald ripening. Rapid crystallization of anhydrous phases, like feldspars, increased the melt water content in the hybrid magma. Eventually, volatile saturation in the hybrid magma was reached that led to the sudden release of volatiles. The sudden release of volatiles or devolatilization event led to resorption of alkali feldspar phenocrysts and stabilizing plagioclase, some of which precipitated around the resorbed phenocrysts to produce rapakivi feldspars.

Detection of metallic prospects using staged factor and fractal analysis in Zouzan region, NE Iran

The Zouzan area is located in the SE of Torbat-e- Heydarieh city (NE Iran). This area is located on north part of the Lut block which consists of basaltic andesite, tuff and porphyritic andesite. The purpose of this research is to investigate the enrichment of metal elements in the Zouzan area and provide a metallic geochemical model. For this purpose, 488 stream samples were analyzed using by ICP-MS. The results were interpreted using staged factor analysis to determine the components that are rich in the study area. However, Concentration-Number (C-N) fractal modeling was used for interpretation of these data and presenting a final model. The results of this study indicate the concentration of anomalies of the Au, Ag, Cu, Pb and Zn as main elements in the central, NE and SW of the Zouzan area. Moreover, results obtained by the staged factor analysis shows the elements of the specified components by this method that enriched together in the study area. The place of enrichment is in the central NE and SW parts of the study area.

Episodic bimodal magmatism at an active continental margin due to Paleo-Pacific Plate subduction: A case study from the southern segment of the Tan-Lu Fault Zone, eastern China

Volcanic rocks in the southern part of the Tan-Lu Fault Zone (TLFZ), eastern China, provide key evidence for the connection between spatially and temporally related pulses of Cretaceous magmatism, activity on the TLFZ, and the dynamics of the Paleo-Pacific Plate. We identify two stages of bimodal volcanism in the Chaohu–Lujiang segment, southern TLFZ, based on lithological assemblages and precise isotopic ages. The Early Cretaceous (125–121 Ma) volcanic rocks are fractionated aluminous A-type rhyolites and basalts, whereas the Late Cretaceous volcanic rocks (97–83 Ma) range in composition from porphyritic andesites and trachydacites to rhyolites. The Early Cretaceous rhyolites display strongly negative Nd-Hf isotopic compositions (εNd(t) = −16.3 to −16.1, εHf(t) = −24.1 to −17.9). The most likely source rocks of the fractionated aluminous A-type rhyolites are metaigneous rocks of the Feidong Complex. The Early Cretaceous potassic basalts (K2O/Na2O = 1.5–3.4, εNd(t) = −9.0) exhibit more enriched isotopic compositions than the Late Cretaceous sodic porphyritic andesites (K2O/Na2O = 0.6–0.8, εNd(t) = −5.6, εHf(t) = −15.1 to −6.8), indicating derivation from heterogeneously enriched lithospheric mantle. This heterogeneity is ascribed to derivation from more fertile and isotopically enriched mantle sources with lower solidus temperatures. Modeling of selected elements reveals that the Late Cretaceous trachydacites (εNd(t) = −12.2 to −8.2, εHf(t) = −16.5 to −6.4) originated by mixing between coeval mafic and felsic magmas. The most negative (εNd(t) = −18.8 to −17.1, εHf(t) = −20.5 to −4.7) isotopic compositions, along with Neoproterozoic inherited zircons within the Late Cretaceous rhyolites, indicate derivation from lower crust of the South China Block. We suggest that the Early Cretaceous bimodal volcanic rocks formed in an extensional backarc setting induced by retreat of the subducting Izanagi slab. However, the TLFZ became a focus of Late Cretaceous bimodal volcanism due to weak far-field extension caused by the slow northward motion of the Paleo-Pacific Plate. Moreover, the high velocity and low angle of subduction of the Izanagi slab were the main driving mechanisms behind an Early Cretaceous transpressional event that separated the two stages of bimodal volcanism.

The Table, a flat-topped volcano in southern British Columbia: Revisited

More than 65 years ago, W.H. Mathews published a seminal paper in American Journal of Science describing the Table, an iconic, flat-topped volcano in southern British Columbia, Canada. The Table is recognized as the type-example of a glaciovolcanic lava-dominated tuya. We use field mapping, 3-D photogrammetry, lithofacies identification and 40Ar/39Ar geochronology to re-examine the emplacement origins of this unique volcanic edifice. The Table is a steep-sided, flat-topped mass of dense, porphyritic andesite preserving a near-original outer surface of hackly fractured aphanitic material. The age of the edifice is 100 ± 12 ka. A new model for the emplacement involves dike injection and endogenous inflation within an overlying ice mass that is estimated to have been ∼250 to 350 m thick. The model assumes that the edifice expanded outwardly as an elliptical cylinder, endogenously inflating and melting an equal volume of ice. The thermal exchange between the expanding massif and the melting ice operates across a subvertical, well-drained, enveloping carapace of quench breccia. For effusion rates of 0.5 to 2 m3 s−1, marginal heat fluxes are 43 to 186 W m−2, implying low overall heat transfer coefficients (0.04 to ∼0.18 W m−2 K−1). The total volume of ice melted serves as a calorimeter and constrains the average thickness (∼3 m) and properties (thermal conductivity; 0.1 – 0.4 W m−1 K−1) of the breccia carapace. The heat transfer efficiency of intermediate lava-dominated tuyas is significantly lower (∼2 %) than reported for other glaciovolcanic systems (commonly ∼45 – 77 %) but similar to that found for block-lava flows and lava tubes.

Geochemistry, fluid inclusions and sulfur isotopes of the Govin epithermal Cu-Au mineralization, Kerman province, SE Iran

Govin area is located southeast of the Urmieh-Dokhtar volcano- plutonic arc, which formed as the result of subduction of the Neo-tethyan oceanic crust beneath the central Iran continent. The arc hosts world-class Sar-Cheshmeh Cu porphyry deposit and many other Cu, Cu-Mo, Cu-Au porphyry, and Cu-Zn-Pb-Ag-Au skarn and epithermal deposits. The rock units in the Govin area include Eocene volcaniclastic rocks that intruded by post-Miocene hypabyssal quartz-monzonite, grano-diorite, diorite and quartz-diorite stocks. The stream sediment geochemical surveys display Cu, Au, Mo, Bi, Sb, Pb and As anomalies. The lithogeochemical prospecting in anomaly checking stage identified quartz veins with considerable abundances of Cu (2.98%) and Au (2.41 ppm). The ore-bearing quartz veins classify into quartz + iron oxides ± gold and quartz + sulfide ± gold. The dominant structural trend of vein systems is 60°–70° (NE-SW), with dips from 75° NW to vertical that cut altered andesite, porphyritic andesite, basaltic andesite and tuff. Mineral associations are quartz, adularia, chalcopyrite, pyrite, bornite, galena, sphalerite, as well as chalcocite, covellite, malachite, iron oxides and hydroxides in oxidized zones. Hydrothermal alteration is generally well-developed surrounding the ore-bearing systems. The main types of alterations in the area include propylitization, phyllic, and argillic associated with silicification. Fluid inclusions studies on quartz grains separated from mineralized veins exhibits the melting temperature of ice (Tm ice) values range from −12 to −1 °C corresponding to salinities of 2.5 to 37.04 wt% NaCl equiv. The superfluity LV fluid inclusions have salinity of 2.47 to 15.96 wt% NaCl equiv. The homogenization temperature of LV, VL and LVS fluid inclusions range from 146 to 366 °C, 405 to 425 °C and 236 to 270 °C, respectively. The fluid inclusions observations reveal that both dilution and boiling of fluids were important in the deposition of metals in the Govin. The δ34SCDT of pyrite and chalcopyrite grains associated with mineralized quartz veins range from −2.13‰ to −8.54‰ that indicate sulfur originated from host volcanic-sedimentary series in the area. The Cu-Au bearing quartz veins in the Govin area are classified as low-sulfidation epithermal system, located in closed association with the Sar-Cheshmeh and Darreh-Zar porphyry copper deposits.

Integrated inversion of airborne geophysics over a structural geological unit: A case study for delineation of a porphyry copper zone in Iran

This work presents the application of an integrated geophysical survey of magnetometry and frequency-domain electromagetic data (FDEM) to image a geological unit located in the Kalat-e-Reshm prospect area in Iran which has good potential for ore mineralization. The aim of this study is to concentrate on a 3D arc-shaped andesite unit, where it has been concealed by a sedimentary cover. This unit consists of two segments; the top one is a porphyritic andesite having potential for ore mineralization, especially copper, whereas the lower segment corresponds to an unaltered andesite rock. Airborne electromagnetic data were used to delineate the top segment as a resistive unit embedded in a sediment column of alluvial fan, while the lower andesite unit was detected by magnetic field data. In our research, the FDEM data were first inverted by a laterally-constrained 1D program to provide three pieces of information that facilitate full 3D inversion of EM data: (1) noise levels associated with the FDEM observations, (2) an estimate of the general conductivity structure in the prospect area, and (3) the location of the sought target. Then EM data inversion was extended to 3D using a parallelized OcTree-based code to better determine the boundaries of the porphyry unit, where a transition exists from surface sediment to the upper segment. Moreover, a mixed-norm inversion approach was taken into account for magnetic data to construct a compact and sharp susceptible andesite unit at depth, beneath the top resistive and non-susceptible segment. The blind geological unit was eventually interpreted based on a combined model of conductivity and magnetic susceptibility acquired from individually inverting these geophysical surveys, which were collected simultaneously.

Caracterización petrográfica, química y edad Ar-Ar de cuerpos porfídicos intrusivos en la formación Saldaña

In the Upper Magdalena Valley, subvolcanic porphyritic andesite and latite rock bodies intrude volcanic lavas and tuffs of the Lower Jurassic Saldana Formation. These rock bodies are characterized by plagioclase phenocrysts up to 2 cm in diameter, together with pyroxene, olivine and sanidine crystals, floating in a hyalocrystalline matrix. They correspond to hypabyssal, alkaline plutons of the metaluminous series, with high alkali content, chemically classified as andesites and interpreted to be generated by subduction in an arc environment, in accordance with their negative Nb and Ti anomalies and LREE/HREE ratios in multielement diagrams. An Ar-Ar plateau age of 159.35 ± 3.55 Ma was obtained in plagioclase, which suggests, along with the chemical characteristics and stratigraphic relationships, that it corresponds to a magmatic event younger than the lavas of the Saldana Formation (186.8 ± 2.0–188.9 ± 1.6 Ma), the Pitalito Vulcanites (168 ± 2.5–172.4 ± 1.7 Ma) and the Jurassic plutons that crop out in the Upper Magdalena Valley (169.4 ± 3–195.8 ± 1.5 Ma).

Relationship between density, compressive strength, tensile strength and aggregate properties of andesites from Hungary

Aggregate properties and strength parameters of four andesites from two operating Hungarian quarries of Nogradkovesd (one lithotype) and Gyongyossolymos (three lithotypes) are presented in this paper. Air-dry, water-saturated and freeze–thaw subjected specimens were tested on core-drilled cylindrical specimens, and the aggregate properties were also determined from the remaining part of the drilled rock blocks. Tensile strength values rapidly decreased from air-dry to water-saturated and finally to freeze–thaw subjected specimens. Linear relationships between air-dry and water-saturated bulk densities and between UCS and modulus of elasticity were found. Micro-fabric influences strength and aggregate parameters of studied andesites; fine porphyritic andesite has the highest UCS and tensile strength and the best micro-Deval results, while coarser porphyritic andesite has lower strength and aggregate parameters. Test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks. A good exponential correlation was found between micro-Deval and UCS values of this paper and previously published data sets, but there was no indication that micro-Deval values correlate well with Los Angeles values.