Iron Ore Bodies Research Articles

Petrogenetic implications, geochemistry and tectonic framework of albitite hosted magnetite in North Delhi Fold Belt: Application of geochemistry and apatite chemistry

The iron ore bodies in the form of lensoidal and pocket type deposits occur within the Meso to Neo-Proterozoic meta-sedimentary rocks and albitites of Ajabgarh Group of Delhi Supergroup in Khetri basin, Western India. These are exposed as detached and linear ore bodies at the southern (western flank) and south-eastern (eastern flank) part of the Khetri copper deposit which follows the regional trend of the host rocks. The detailed field and petrographic studies reveal that the magnetite and hematite are associated with major silicates like quartz, actinolite, muscovite, biotite, albite and, K-feldspar. Some minor occurrences of apatite, sphene, ilmenite and monazite are also found. This work is focused on understanding the evolution of albitite-hosted magnetite with respect to tectonic signatures, the source of mineralizing fluid, and its spatial relationship with the regional albitites and meta-sediments. To interpret the above, whole rock geochemistry of albitite rocks, magnetite ore and mineral chemistry of fluorapatite, were adopted.The whole rock geochemistry of albitite suggests that the parent rocks are of calc-alkaline magma series that are originated from the subduction-related rift zone of volcanic arc environment. The apatite chemistry signifies that these are evolved from the highly fractionated granitic rocks (granitoid) at moderate to high oxidizing conditions. Some deformed apatite grains are also encountered having small distorted monazite inclusions. Thus, it has an indication of high-temperature metasomatic/hydrothermal fluids that may be responsible for the removal of REEs from apatite and re-nucleate as monazite inclusions within it. Therefore, the overall evidence and associations of albitite with apatite-magnetite is demonstrating that the source rock of the study area could have evolved from the arc system of active continental margin which was abundant with Fe, U, REEs, etc. Hence, the sources rocks were suitably metasomatized by hydrothermal fluids channelized through the regional shear zone and simultaneous precipitation of the magnetite in the study area. The dominance of magnetite, associated REEs, apatite, and non-association of sulfide minerals with the magnetite in the area of study has close similarities with the IOA type deposits.

Elucidating the Genetic Mechanism and the Ore-Forming Materials of the Kaladawan Iron Deposit in the North Altyn Tagn, Western China

The Kaladawan iron deposit is located in the North Altyn Tagh and exhibits occurrences of iron ore bodies at the contact zone between Ordovician magmatic rocks (basalts, rhyolite, and granodiorite) and marble. However, controversy persists regarding the genetic classification and metallogenic mechanism of this deposit. Through a field investigation, single mineral in situ geochemical analysis, whole-rock geochemical analysis, and Fe isotope determination, the following conclusions are made: (1) Ti-(Ni/Cr) and (V/Ti)-Fe diagrams indicate that the magnetite from all studied rocks underwent hydrothermal metasomatism, while (Ni/(Cr + Mn))-(Ti + V) and (Ca + Al + Mn)-(Ti + V) diagrams suggest a skarn origin for these magnetites. Therefore, it can be inferred that the Kaladawan iron deposit is skarn-type. (2) The iron ore exhibits similar rare-earth-element characteristics to the altered basalt. Additionally, the altered basalts (δ56Fe = 0.024~0.100‰) are more enriched in light Fe isotopes than the unaltered basalts (δ56Fe = 0.129~0.197‰) at the same location, indicating that the ore-forming materials of the Kaladawan iron ore are mainly derived from basaltic rocks. (3) According to the law of mass conservation and the intermediate Fe isotopic composition of the iron ore between the granodiorite and basalt, the hydrothermal fluid for the formation of iron ores was inferred to be derived from the late intrusive granodiorite.

Activation of Seismo-Acoustic Events after Large-Scale Blasting at an Iron Ore Body of the Kursk Magnetic Anomaly

Activation of Seismo-Acoustic Events after Large-Scale Blasting at an Iron Ore Body of the Kursk Magnetic Anomaly

Cobalt distribution and enrichment in skarn iron deposits: A case study of the Zhuchong skarn iron deposit, Eastern China

Global Cobalt (Co) is mainly mined from sediment-hosted, magmatic sulfide, or laterite deposits, but rarely in skarns. The Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB), eastern China, is an important skarn iron ore producer, where skarn iron deposits are often associated with Co. The Zhuchong iron deposit is a typical high-grade skarn iron deposit with Co enrichment in this belt. This deposit contains 50 Mt Fe ore @50.1 %, 4.3 Mt Cu ore @1.15 %, and ∼ 10000 t Co metal with an average grade of 0.019 %. In this study, the distribution and enrichment of Co at Zhuchong were investigated by detailed petrographic observations, mineral geochemistry, and whole-rock major and trace element data. Our results indicate that Co contents in the ore and gangue minerals at Zhuchong follow these trend: pyrite (median = 2138 ppm) > pyrrhotite (705 ppm) > sphalerite (352 ppm) > magnetite (72.1 ppm) > diopside (42.5 ppm) > chalcopyrite (3.11 ppm) > garnet (1.23 ppm). The negative correlation between Co + Ni and Fe in pyrite suggests that the incorporation of Co into pyrite can be achieved by the substitution mechanism of 2Fe2+ ↔ Co2+ + Ni2+. Depth profile analysis reveals that the Co-enriched pyrite is mainly developed in the contact zone between the diorite pluton and the skarn iron ore body. Pyrite far from the pluton has lowered Co contents ranging from several to hundreds ppm. This study highlights that the enrichment of Co in pyrite at Zhuchong is probably temperature-dependent. Co/Ni ratios of pyrite range from 0.01 to 10000, and where pyrrhotite occurs the ratios increase. Additionally, Our results establish pyrite as the primary carrier of Co at the Zhuchong deposit, contributing approximately 5000 tons of Co. Pyrrhotite and magnetite account for about a quarter proportion of total Co reserves, respectively. Our study emphasizes that finding out the Co-rich location and its occurrence nature of the deposit is of great significance for the recovery and utilization of Co in skarn iron deposits.

Iron ore to lodestone: With lightning assist

A lodestone is a piece of magnetite or titanomagnetite iron ore having an extremely intense remanent magnetization; it is nature's only permanent magnet. This magnetization intensity is larger than could be acquired in any iron ore by any known natural mechanism through exposure to just the Earth's magnetic field. This is revealed by the large ratio (REM) of the measured (NRM) - natural remanence, to the (SIRM) - saturation remanence.We describe new details of the mechanism by which part of an iron ore body becomes a lodestone: Exposure to lightning bolt related electric discharge's magnetic fields is required.While the lightning bolt related magnetic fields are necessary, they are not sufficient for creation of a lodestone. We show that the iron ore must be previously magnetically “hardened” into what we term a “latent lodestone iron ore” condition before the transformation to lodestone can be achieved.A magnetic hardness continuum (characterized with magnetic hysteresis loop parameters) for a range of magnetite and titanomagnetite iron ores demonstrates how the hardening is created by alteration; in magnetite through oxidation scenarios and in titanomagnetite by solid state exsolution and oxidation.Large REM (evidence of lightning), the *Polarity signature (which we identify with iron powder patterns) reflecting the large REM, and the location on the magnetic hardness continuum (latent lodestone state resulting in largest possible magnetization), provides important details to the lodestone story.

Oxygen Isotopes of Iron Oxides as a Diagnostic Tool for Iron Formation-Hosted High-Grade Magnetite-Hematite Deposits

Coarse-grained granoblastic magnetite-hematite and sheared platy hematite iron orebodies comprise several small deposits (5 to 30 Mt each) on the eastern margin of the São Francisco Craton, bordering the Ediacaran–Cambrian Brasiliano Orogenic belt. Three main mineralization stages are associated with the Brasiliano Orogeny: (1) syn- to the late-collisional stage (ca. 580–560 Ma) with development of lens-shaped schistose orebodies along thrust planes. (2) late- to the post-collisional stage (ca. 560–530 Ma) with the formation of massive magnetite bodies by contact metamorphic-metasomatism with pegmatite. (3) Post-tectonic stage with crystallization of granular hematite associated with late pegmatite (ca. 530–490 Ma). In order to better evaluate the fluid oxygen signature of each mineralization stage, new oxygen isotopes measurements were performed on ore bodies associated with the three stages. These stages are followed by changes in the oxygen isotope signature, with a progressive decrease of the δ18O from the iron formation (1.7 to 8.1‰) to high-grade ore (-1.6 to 2.6‰) that appears to be a common aspect of the mineralization of iron formations. In the present cases, magmatic fluids (δ18O from 4.6 to 13.1‰) have imprinted a relatively “heavier” signature than the most hypogene iron formation high-grade ores worldwide that was progressively modified by meteoric water percolated along extensional fractures. The iron oxides from the contact zones of pegmatitic yielded intermediate δ18O values (1.8 to 5.0‰), indicating a higher magmatic fluid/rock ratio.

The genesis of acid alteration in the Luohe IOA-type deposit, Eastern China and its constraints on mineralization

Luohe is the largest IOA-type deposit in the Middle and Lower reaches of the Yangtze Metallogenic belt. The iron ore body is hosted in thick volcanic rocks, and widespread acidic alteration (secondary quartzite) developed at shallow depths, providing an excellent opportunity to study the genesis of acidic alteration rocks and the genetic links with the IOA mineralization. In this study, detailed mineralogy, in situ sulfur isotopes, and trace element analyses were performed on pyrite from a shallow drill hole in the Luohe deposit. The results indicate that the formation time of acidic alteration is between magnetite (stage II) and anhydrite-pyrite (stage IV), with pyrite sulfur isotopes ranging from −14 to 4‰, which is significantly different from those in stage IV (7-9‰). The anomaly negative sulfur isotope suggests the existence of SO2 disproportionation reaction, and the δ34S of pyrite increases with depth decrease, ultimately falling within the mantle sulfur range. This indicates that the sulfur origin of acidic alteration pyrite is a single magma sulfur source, which is significantly different from the deep iron mineralization system (magmatic + evaporite). The trace elements Co, Ni, As, Ti, Cu, Sb, Tl in pyrite indicate that the acidic alteration fluid has the characteristics of low temperature, low pH, and is rich in F and Cl. Combined with the sulfur isotope results, it is believed that pyrite in the acidic alteration rock of the Luohe was formed by the mixing of gaseous SO2 and shallow groundwater, which is a part of the Luohe magmatic-hydrothermal mineralization system and an important indication for regional exploration of similar deposits.

Cadomian Iron ore bodies in the Bafq-Saghand metallogenic province, Iran: genetic constraints from field observations and laser ablation ICP-MS mineral studies

ABSTRACT The volcano-sedimentary unit in the Bafq-Saghand metallogenic province (BSMP) of Central Iran hosts various types of iron ore bodies including Fe-oxides with jaspilite beds, Mn-dominated iron lenses, magnetite-apatite lenses, and massive magnetite-apatite deposits. The Fe-oxides with jaspilite beds and Mn-dominated iron lenses have limited outcrops and show volcano-sedimentary features in the field. The main features are the presence of syngenetic submarine rhyolite-hosted magnetite, lamination and bedding of iron ore body, jaspilite and dropstone. Volcano-sedimentary origin is testified by magnetite composition showing affinity to BIF and positive Eu and negative Ce anomaly. Magnetite-apatite lenses and massive magnetite-apatite deposits that having spatio-temporal correlation form the main economically important deposits. They have magmatic to high-temperature hydrothermal field characteristics (lava flow-like ore bodies, the presence of degassing tubes in ore bodies, occurrence of brecciated texture and developed Na-Ca metasomatism). Mineral composition (enrichment of LREE, magnetite and apatite negative Eu anomaly and Co/Ni < 1 in pyrites) is in agreement with magmatic and high temperature hydrothermal origin. We propose a hydrous and oxidizing mantle derived iron-rich basic magma that formed in an extensional post-collisional setting for origin of Kiruna-type IOA ore bodies of the BSMP. Fe-oxides with jaspilite beds and Mn-dominated iron lenses resulted from degassing or eruption of iron-rich magma during Ediacaran in a submarine environment. However, magnetite-apatite lenses and massive magnetite-apatite deposits formed from an Early Cambrian magmatic-hydrothermal transition system from a magnetite-crystal mush zone.

Chronolgy and Geochemistry of the Sijiaying Iron Deposit in Eastern Hebei Province, North China Craton: Implications for the Genesis of High-Grade Iron Ores

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al2O3 and TiO2 and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO2 and Al2O3, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores.

Origin and evolution of the ore-forming fluids in the southern Abbas Abad iron skarn deposit, NE Isfahan, Central Iran: Insights from geology, fluid inclusions, and C[sbnd]O isotopes

The southern Abbas Abad iron skarn deposit is located in the western part of the Central Iran zone, SW edge of the Urumieh˗Dokhtar magmatic arc. The skarn alteration occurred mainly at the contact of the Abbas Abad gabbro and Triassic Nayband Formation. The Triassic Nayband Formation in the southern Abbas Abad area consists of limestone, shale, siltstone, and marl with interlayers of tuff. The Abbas Abad gabbro is calc˗alkaline with adakitic signatures and continental arc setting affinity. Four iron ore bodies occur along the NW˗SE trending normal fault along the southern margin of Abbas Abad gabbro within sedimentary host rocks of the Nayband Formation. Three main paragenetic stages of skarnification and ore deposition have been recognized: i) prograde stage, ii) retrograde stage, and iii) supergene stage. Spinel, garnet, and pyroxene formed during the prograde stage. Epidote, tremolite˗actinolite, calcite and ore minerals, such as magnetite, hematite-I, pyrite, and minor chalcopyrite formed the retrograde stage assemblage. Magnetite is the main economic ore mineral, which is diverse in terms of fabric and texture, including massive, disseminated, needle˗like, blade˗like, prismatic, crustification, and cubes. Stable isotope data from Abbas Abad iron skarn deposit indicated that the interaction of non-magmatic brine (connate) fluids with Triassic carbonate host rocks at high temperature and its mixing with meteoric water has led to changes in the isotopic composition of the mineralizing fluid. Subsequently, garnet and magnetite with relatively high estimated fluid δ18O values (average 12.3 and 14.6 ‰, respectively) formed from this modified fluid. The estimated δ18O values of fluid in equilibrium with calcite decreased as a result of the greater influx of the meteoric water into the hydrothermal system in the late stages of ore formation. Fluid inclusion data from this iron skarn deposit are consistent with minor boiling during the prograde stage, although cooling and dilution seem to be principally responsible for Fe precipitation. The petrogenetic model proposed for the Southern Abbas Abad iron skarn deposit suggests that during the Eocene a gabbroic stock intruded the sedimentary rocks of the Nayband Formation and acted as a heat source for the non-magmatic brine (connate and meteoric) fluids convection cells, then reacted with cooler Triassic carbonate rocks. In this model, leaching of the gabbroic rock provided the iron, whereas carbon came from degassing and dissolution of carbonate rocks during contact metamorphism-metasomatism.

The Use of Remote Sensing Technology in Geological Investigation and Mineral Detection in Ban Vang area, Kham District, Xieng Khoang Province, Laos

Ban Vang area, Kham District, Xieng Khouang province, Laos is interested by many geologists. Remote sensing analytical results have identified some prospective mineral areas. One of them is the Ban Vang area. On that basis, Indochina Mining Joint Venture Company (IMC) cooperated with the Northwest Geological Division (Ministry of Natural Resources and Environment of Vietnam) to conduct mineral exploration in the Ban Vang area. The research results suggest that the Ban Vang area, Kham District, Xieng Khouang province, Laos has 2 iron ore bodies, 3 copper ore bodies, and potential ore outcrops. The Fe content of the iron orebodies varied from 28.5% to 58.7%. The ore-bearing rocks and the adjoining rocks are gray skarns having a solid structure with the main mineral composition of pyroxene and garnet. The copper content of the copper orebodies ranged from 0.14% to 5.59%. Copper ore bodies’ bedding is inclined to the west with a dip angle from 55o to 85o and thickness from 0.7m to 20.59m. The ore-bearing rocks and adjoining rocks are gray metamorphic rocks (skarn) with massive structure, granule, panidiomorphic, and grain textures. The mineral composition is mainly garnet and pyroxene. This article introduces remote sensing applications of mineral search in the Ban Vang area. The mineral search was conducted by the Northwest Geological Division. In this project, the author is a supervisor of the IMC Company.

Geochronology and geochemistry of zircons from fertile and barren intrusions in the Sangan mining area (NE Iran): Implications for tectonic setting and mineral exploration

The Sangan mining area is the largest Cenozoic skarn iron ore district in the far eastern part of the Alborz Magmatic Arc in Iran. In this study, we evaluate the zircon composition as an important exploration tool and pathfinder for skarn mineralization to elucidate distinctive zircon signatures diagnostic of metallogenic fertility of the parent magma. Granitoid intrusions in the Sangan mining area are subdivided into the fertile Sarnowsar intrusion composed of syenite, syenogranite, and granite and the barren Sarkhar and Bermani intrusions composited of monzogranite and syenogranite. The Eocene Sarnowsar intrusion was produced by the flare-up magmatism and is an oxidized I-type granitoid suite. Fourteen iron ore bodies occur along the contact of this intrusion with the carbonate country rocks. In the barren Sarkhar and Bermani intrusions, monzogranites have zircon U-Pb ages of 41.7 ± 0.6 Ma and 41.9 ± 0.3 Ma, whereas syenogranites have ages of 37.8 ± 0.3 Ma, 37.9 ± 1.7 Ma, and 37.4 ± 1.8 Ma. These ages span the same time interval as the Eocene flare-up occurrences throughout Iran.

Copper mobilization via seawater-volcanic rock interactions: New experimental constraints for the formation of the iron oxide Cu-Au (IOCG) mineralization

The involvement of modified seawater and/or basinal brine in IOCG mineralization was documented by numerous geologic studies. Still, this process remains poorly understood. In this study, we reacted seawater with andesite and basalt, the most common arc volcanic rocks, at 150 and 240 °C and water vapor-saturated pressure to assess the Cu leaching capacity and fluid evolution due to the seawater-volcanic rock interactions. The experimental results show that Mg, Fe, Al, and SO42− in the modified seawater decreased significantly, accompanied by an increased Ca concentration. The fluid pH also decreased from 8.3 of the initial seawater to ∼7.5 and ∼7.0 after 150 and 240 °C experiments, respectively. The incongruent calcsilicate (e.g., plagioclase) dissolution and anhydrite precipitation were observed in the reacted rock samples. Thermodynamic modeling confirmed the trends of those concentration changes but predicted several alteration minerals that were not observed in the experiments. Our experiments show that Cu-leaching efficiency is much higher from the andesite than from the basalt, also higher at 240 °C than at 150 °C. The andesite contains more Cu than the basalt samples, and abundant Cu-rich (average 106 ppm) plagioclase-hosted silicate melt inclusions and Cu-bearing (average 59 ppm) groundmass are identified in the original andesite sample but not in the original basalt sample, which is considered to be the cause of the Cu-leaching differences between the two rock samples. The δ34S value of resultant fluids is dominated by seawater sulfate with a minor contribution of magmatic sulfur from the rock. Thermodynamic modeling combined with recent experimental studies show that deposition of Cu sulfides is the most effective when Cu-bearing fluids react with early-stage pyrite. Our results suggest that the seawater/(brine)-volcanic rock reactions at 150–250 °C can produce Cu-bearing fluids, which in turn can form IOCG deposits, and that Cu mineralization with sulfides zonation can result from replacement reactions between the Cu-bearing fluids and Fe-rich minerals in precursor iron ore bodies.

Superimposed zinc and gold mineralization in the Dunde iron deposit, western Tianshan, NW China: Constraints from LA-ICP-MS fluid inclusion microanalysis

The submarine volcanogenic iron oxide (SVIO) deposits are one of the most important sources of high-grade iron ores in China. Many large- and medium-scale SVIO deposits were recently discovered in the Awulale metallogenic belt (AMB) in Western Tianshan, NW China. The Dunde deposit in the AMB is a unique iron deposit containing large-scale Zn and medium-scale Au resources. The zinc mineralization in this deposit is generally located at the margin of iron orebodies constituting composite iron-zinc orebodies. To clarify the genetic relation between iron and Zn with Au mineralization, we conducted a detailed investigation of sphalerite-hosted fluid inclusions in the Dunde deposit. The primary fluid inclusions in sphalerite are liquid-rich, with homogenization temperature in the range of 189–219 ℃, and salinity of 19.68–22.38 wt% NaCl equiv. Single fluid inclusion LA-ICP-MS analysis suggests a magmatic source for the fluid as reflected by high Rb/Na (0.001–0.016), K/Na (0.18–0.83) and low Ca/K (1.03–9.38) ratios, which are distinctly different from those of basinal brines. The Cs/(K + Na + Ca)*10000 values (6.0–13.4) of sphalerite-hosted fluid inclusions are equivalent to those in porphyry-type Cu-Mo deposit (4.7–23.8), indicating that the ore-forming fluid originated from a highly evolved granitic magma, rather than intermediate-mafic magmatism related to iron mineralization. Thus, we propose that the zinc and gold mineralization in the Dunde deposit might be products of superimposed mineralization on iron orebodies during hydrothermal alteration related to granitic intrusions.

Discovery of iron orebodies in the Dahalajunshan Formation carbonate rocks in the Beizhan volcanic-hosted iron deposit, Xinjiang and its genetic significance

Discovery of iron orebodies in the Dahalajunshan Formation carbonate rocks in the Beizhan volcanic-hosted iron deposit, Xinjiang and its genetic significance

Zircon U-Pb and molybdenite Re-Os geochronology and geochemistry of the Tieling deposit in the Eastern Tianshan, NW China: Insights into the timing of mineralization and tectonic setting

The Aqishan-Yamansu belt in the Eastern Tianshan (NW China) contains many Carboniferous granitic intrusive rocks and volcanic rocks and hosts numerous large to medium sized Fe (-Cu) deposits. The Tieling deposit consisting of 89 iron ore bodies in the Aqishan-Yamansu belt has been mined since discovered in 1970 s. Mo mineralization was newly identified in concealed rocks of the Tieling deposit, and molybdenite is extensively distributed as a disseminated phase in the biotite moyite and occurs as aggregates in quartz veins. The molybdenite Re-Os model ages (300.6 ∼ 298.7 Ma) are consistent with the zircon U-Pb age (304.5 ± 2.4 Ma) of the ore-causative biotite moyite within error, which indicating that the Tieling Mo mineralization occurred during the Late Carboniferous. The Late Carboniferous biotite moyite exhibits calc-alkaline and peraluminous characteristics, with negligible Eu anomalies, akin to I-type granites. Dominantly positive εHf(t) values (+13.6 to + 15.2), variable Mg# values (31 to 49), and limited variation in (87Sr/86Sr)i ratios (ISr = 0.70358–0.70390), and positive εNd(t) values (+4.55 to 6.39), along with the juvenile TDM2 age (548 to 697 Ma), suggest that the biotite moyite was probably originated from partial melting of the juvenile lower crust with involvement of mantle-derived magmas. Integrating published data and our work, we conclude that the Aqishan-Yamansu belt evolved from the pre- Early Carboniferous forearc basin (ca. 450–350 Ma) to the Carboniferous island arc environment (ca. 350–310 Ma) triggered by the bidirectional subduction of the Kanggur Ocean, then the extensional geodynamic setting (ca. 310–270 Ma) is conducive to the porphyry Mo mineralization of the Tieling deposit and Ni-Cu-Au deposits in the Eastern Tianshan.

Numerical modeling of mineralizing processes during the formation of the Yangzhuang Kiruna-type iron deposit, Middle and Lower Yangtze River Metallogenic Belt, China: Implications for the genesis and longevity of Kiruna-type iron oxide-apatite systems

The Yangzhuang iron deposit is a Kiruna-type iron oxide-apatite (IOA) deposit within the Ningwu mining district of the Middle and Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study applies a numerical modeling approach to identify the key processes associated with the formation of the deposit that cannot be easily identified using traditional analytical approaches, including the duration of the mineralizing process and the genesis of iron orebodies within intrusions associated with the deposit. This approach highlights the practical value of numerical modeling in quantitatively analyzing mineralizing processes during the formation of mineral deposits and assesses how these methods can be used in future geological research. Our numerical model links heat transfer, pressure, fluid flow, chemical reactions, and the movement of ore-forming material. Results show that temperature anomaly and structure (occurrence of the contact of intrusion and the Triassic Xujiashan group) are two key factors controlling the formation of the Yangzhuang deposit. This modeling also indicates that the formation of the Yangzhuang deposit only took some 8000 years, a reaction that is likely to be controlled by temperature and diffusion rates within the system. The dynamic changes of temperature and the distribution of mineralization also indicate that the orebodies located inside the intrusions most likely formed after magma ascent rather than representing blocks of existing mineralization that descended into the magma as a result of stoping or other similar processes. All these data form the basis for future research into the forming processes of Kiruna-type IOA systems as well as magmatic–hydrothermal systems more broadly, including providing useful insights for future exploration for these systems. The simulation approach used in this study has several limitations, such as oversimplified chemical reactions, uncertainty of pre-metallogenic conditions and limitation of 2D model. Future development into both theories and methods will definitely improve the practical significance of numerical simulation of ore-forming processes and provide quantitative results for more geological issues.

Highly efficient density inversion of gravity data using nonlinear density polynomial fitting

The density inversion of gravity data is commonly achieved by discretizing the subsurface into prismatic cells and calculating the density of each cell. During this process, a weighting function is introduced to the iterative computation to reduce the skin effect during the inversion. Thus, the computation process requires a significant number of matrix operations, which results in low computational efficiency. We have adopted a density inversion method with nonlinear polynomial fitting (NPF) that uses a polynomial to represent the density variation of prismatic cells in a certain space. The computation of each cell is substituted by the computation of the nonlinear polynomial coefficients. Consequently, the efficiency of the inversion is significantly improved because the number of nonlinear polynomial coefficients is less than the number of cells used. Moreover, because representing the density change of all of the cells poses a significant challenge when the cell number is large, we adopt the use of a polynomial to represent the density change of a subregion with fewer cells and multiple nonlinear polynomials to represent the density changes of all prism cells. Using theoretical model tests, we determine that the NPF method more efficiently recovers the density distribution of gravity data compared with conventional density inversion methods. In addition, the density variation of a subregion with 8 × 8 × 8 prismatic cells can be accurately and efficiently obtained using our cubic NPF method, which also can be used for noisy data. Finally, the NPF method is applied to real gravity data in an iron mining area in Shandong Province, China. Convergent results of a 3D perspective view and the distribution of the iron ore bodies are acquired using this method, demonstrating the real-life applicability of this method.

Justification of process flows and designs for mining blind ore bodies in the vicinity of mined-out voids

The trending deep-level mining governs substantial alteration of geomechanical situation in mines. The key approach to the stress&ndash;strain behavior assessment in rock mass when predicting and preventing geodynamic events is the geomechanical analysis of the rock mass behavior in the course of mining. The rockburst-hazardous mining research can use such methods as microseismic investigation, acoustic micromeasurements, electrometry, deformation monitoring, etc. The authors have accomplished the stress&ndash;strain behavior assessment in rock mass during mining at rockburst-hazardous deposits of Tashtagol and Sheregesh. The process solutions on underground mining in high-stress rock mass are analyzed. The process flow charts are developed. Alternative stoping technologies are identified, and the design data of mining systems for blind ore bodies are justified. It is shown that safe and efficient mining of blind iron ore bodies in the vicinity of mined-out voids in rockburst-hazardous conditions is achievable using: room-and-pillar mining, with rooms arranged across the strike of an ore body, and with subsequent transition to sublevel caving with levels 70 m high and sublevels 25&ndash;30 m high; shrinkage stoping and bulk caving; cut-and-fill method with cemented backfill. It is found that in top-downward mining of blind ore bodies, the transition from the room-andpillar system to sublevel caving and cut-and-fill method ensures reduction in ore loss and dilution by 1.1&ndash;1.5 and 7.5&ndash;10 %, respectively.

Geology and trace element geochemistry of the albitite hosted iron ore mineralization around Khetri copper deposit, India: Implications for an IOA type deposit

Numerous occurrences of medium to high grade (44.1 to 65 wt%) pocket type iron ore bodies within the Meso to Neo-Proterozoic albitites and meta-sedimentary rocks are exposed around the south and south-eastern part of the Khetri copper deposit, India. The magnetite-hematite rich iron ore bodies occur as massive, and vein fillings within the albitites/albitized phyllite host. Apatite, sphene, monazite, and REE phases are also associated with iron ore minerals. Sporadic albitite, pegmatite, and quartz-carbonate-fluorite veins are also intruded into the iron ore bodies. The V concentration with <1000 ppm (average 644 ppm) and lower value of Ti (average 88.79 ppm), Cr (average 196.58 ppm), Co (average 84.28 ppm) content measured by Laser Ablation ICP-MS and EPMA, suggest a significant role of the hydrothermal/metasomatic activity for the precipitation of magnetite in the study area. Further, relatively higher Ni/Cr (>1) ratio of magnetite from the study area signifies that the rate of solubility and mobility of Ni is more than Cr in a high-temperature hydrothermal fluid. Fe vs V/Ti plot refers towards the hydrothermal origin of the magnetite and Sn/Ga vs. Al/Co diagram suggests the magnetites have the signature of IOCG deposits. The multi-trace element variation diagram of magnetite is also analogous to the high-temperature hydrothermal origin like IOCG-IOA type deposits. Based on the chemistry, mineral association, and spatial occurrence of the magnetite with albitites (product of Na-metasomatism), the magnetite are considered to have deposited during the regional soda-metasomatism and classified under Iron Oxide Apatite (IOA) clan.