Iron Oxide-apatite Deposits Research Articles

Combination model-based numerical simulation of the mineralizing processes within iron oxide-apatite systems

Iron oxide-apatite (IOA) deposits are high grade iron magmatic-hydrothermal mineral deposits having significant economic values and extremely complex and coupled forming processes. The combination model of ore deposits is a model integrating characteristics of several deposits with the same genetic type or sharing close temporal-spatial correlations. This research highlights the usage of numerical simulation method and combination model of deposits in quantitatively analyzing ore-forming processes during the formation of IOA systems and views the future developments of numerical modeling in ore geology research. Our numerical model couples heat transfer, pressure, fluid-flow, chemical reactions and migration of ore-forming materials. Results match the fact that temperature reduction and pressure variation are two key factors controlling the temporal-spatial distribution of iron mineralization, and results of cooling process indicates that a single period of ore formation of IOA deposits may last no more than 12,200 years, a timespan much shorter than previously estimated. These results are obtained based on the concept of combination model of IOA systems, providing quantitative information reflecting the generation of IOA deposits. However, the methods in our research are stills limitations remained, such as uncertainty of pre-metallogenic conditions and restriction from elementary reactions. Future advances in analytical methods and mathematical models will definitely improve the practicality of combination model of deposits and numerical modeling of ore formation, and provide quantitative answers for existing problems related to mineral deposits.

Textural and compositional constraints on the origin, thermal history, and REE mobility in the Lakeh Siah iron oxide-apatite deposit—NE Bafq, Iran

Textural and compositional constraints on the origin, thermal history, and REE mobility in the Lakeh Siah iron oxide-apatite deposit—NE Bafq, Iran

Zircon U–Pb ages, Hf-O isotopes and trace elements of the multi-volcanism in the Ningwu ore district, eastern China: Implications for the magma evolution and fertility of iron oxide–apatite (IOA) deposits

The Ningwu ore district is the best-defined iron oxide–apatite (IOA) district in China and hosts >30 IOA deposits. At Ningwu, four volcanic cycles occurred over a short period of ∼ 10 Ma and yielded comparable lithogeochemical characteristics. However, only the sub-volcanic intrusive rocks from the Dawangshan Formation are associated with IOA-type mineralization. In this study, the mineralization related and unrelated formations have been distinguished based on zircon Hf-O isotope and trace element analyses to reveal the magma evolution and fertility of IOA deposits. Our results suggest that the Mesozoic volcanic rocks at Ningwu have three components of sources: enriched mantle, Archean crystalline basement, and Neoproterozoic crustal materials. The main sources for the magmas of the Longwangshan and Dawangshan formations include the Archean crust and enriched mantle, whereas those for the Gushan and Niangniangshan formations include Neoproterozoic crust and enriched mantle. According to the magmatic sources, the four volcanic formations in the Ningwu ore district can be divided into two groups: (1) the Longwangshan and Dawangshan formations and (2) the younger Gushan and Niangniangshan formations. The magmatic oxygen fugacities (fO2) for the Longwangshan and Dawangshan formations are ΔFMQ +0.6 to +2.2 and ΔFMQ +0.8 to +3.0, respectively. In comparison, the Gushan Formation has much lower magmatic fO2 values of ΔFMQ +0.2 to +0.6, whereas the Niangniangshan Formation yielded magmatic fO2 values peaking at ΔFMQ +0.6 to +2.4 and +3.2 to +4.2. Our new data, together with previous results, suggest that moderate magmatic fO2 (ΔFMQ +0.8 to +3), F-richness, high water contents, high proportions of enriched mantle materials, and a higher degree of magma evolution may affect the fertility of the magma for IOA deposit formation.

Multivariate statistical analysis of trace elements in apatite: Discrimination of apatite with different origins

Partial least squares-discriminant analysis (PLS-DA) was used to construct the link between trace element contents of magmatic or hydrothermal apatite and deposit and rock types. Apatite with different origins is discriminated by characteristic chemical composition. In average, ore magmatic apatite has higher light REE and Th, and lower Sr than barren rock apatite, independent of deposit types. Hydrothermal apatite has lower La, Ce, Pr, and Nd contents than magmatic apatite, probably because fluids prefer migrating light rare earth element out of apatite. Hydrothermal apatite from iron oxide copper gold (IOCG) and iron oxide apatite (IOA) deposits is discriminated by high Mn and Sr relative to magmatic apatite, probably because these elements are fluid mobile. Barren magmatic apatite from granitoid-related deposits is well separated from ore magmatic apatite by higher Sr, Eu, Gd, Tb, Dy, and lower Mn contents, which are likely related to the relatively low degree of differentiation and high aluminum saturation index of parental magma.Magmatic apatite from IOA deposits is discriminated by relatively high Nd, Sm, Gd, Tb, Dy, and low Mn and U contents, which are possibly related to the crystallization of Mn-compatible magnetite microlites and peraluminous magmas. Magmatic apatite from granitoid-related W deposits is relatively rich in Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The relative enrichment of Sr in magmatic apatite from granitoid-related Cu-Pb-Zn and Pb-Zn deposits is likely due to less fractionation of Sr-compatible plagioclase. Melt of sediment component accounts for high Mn and Th in magmatic apatite from granitoid-related Mo deposits. Magmatic apatite from porphyry deposits is discriminated by relatively high V, Sr, and Eu contents. Magmatic apatite from porphyry Mo deposits has relatively high Pr, Nd, and Sm and low Sr contents compared to other types of porphyry deposits due to the more evolved magma. Hydrothermal apatite from IOA deposits is discriminated by high V and Sr, whereas those from IOCG deposits have high Sm, Eu, Gd, Tb, and U contents, because the lower temperature of IOCG cause precipitation of REE in Cl-rich fluid. Relatively low Gd and Tb in hydrothermal apatite from skarn deposits are possibly due to the crystallization of amphibole.Apatite in carbonatite has high contents of trace elements possibly because high contents of Ca and P in melts cause high apatite-melt partition coefficients of trace elements. Apatite from sedimentary and metamorphic rocks is discriminated by relative enrichment of Sr and Eu. Compared to igneous rocks, apatite from sedimentary rocks has low REE contents, reflecting low REE budget in surface waters. Breakdown of some minerals to release and remobilize REE and U during metamorphism can interpret high heavy REE and U contents in apatite from high-grade metamorphic rocks relative to those from low- and medium-grade metamorphic rocks. The ability to discriminate apatite from different types of deposits and rocks indicates the application potential of apatite chemistry in mineral exploration. A flowchart was proposed to identify apatite with unknown origins.

Systematic textural and geochemical variations in magnetite from a porphyry-skarn Cu (Au) system and implications for ore formation, perspective from Xinqiao Cu-Fe-Au deposit, eastern China

Magnetite is an abundant mineral in both porphyry ore and related skarn ore; the physical and chemical characteristics of magnetite in different parts of mineralized zones may allow determination of the related ore-forming processes. We present the results of detailed textural and chemical studies of magnetite from Xinqiao porphyry-skarn Cu-Au deposit, eastern China, to constrain the causative magmatic-hydrothermal processes.Five types of magnetite are identified, magmatic magnetite (type1) occurs in the causative quartz monzodiorite intrusion; re-equilibrated magmatic magnetite (type2) occurs in endoskarn; hydrothermal magnetite aggregated with hydrothermal biotite (type3a) or disseminated (type3b) and veins (type3c) occurs in the porphyry alteration zone; massive magnetite (type4) and disseminated or banded magnetite (type5) occurs in the exoskarn. Magmatic magnetite with oxy-exsolution of ilmenite lamellae indicates the magma was oxidized, and type1 magnetite that underwent hydrothermal re-equilibration (replaced by titanite and hematite) to form type2 magnetite indicates that the early magmatic-hydrothermal fluid was high temperature and highly oxidized during endoskarn formation. The Ti-rich type3a-c magnetite and the presence of ilmenite-rutile lamellae in type3c magnetite from the porphyry alteration zone demonstrate Ti mobility in the porphyry ore-forming fluid, which was high T (450 °C), oxidized and volatile-rich (hydrothermal fluorapatite; F > 3.0 wt%). Trace elements Ti, V, Sc, Co, Ni are positively correlated and decrease from type3 to type5; Mg, Mn, Zn increase in the same sequence, consistent with the temperature of fluid decreasing from porphyry to skarn mineralization, and increasing fluid-rock interaction. The elevated Sn in type5 magnetite and its coexistence with hematite in the retrograde skarn zone also indicate that the fluid remained oxidized during early skarn ore formation. Crystallization of magnetite increased the supply of reduced sulfur, which assisted formation of the Cu mineralization at Xinqiao. We highlight that magnetite textures and compositions can effectively trace the ore-forming processes in porphyry-skarn deposits, and show that porphyry related skarn magnetites are distinguishable from those in skarn Fe, skarn Cu, IOA (iron oxide-apatite) and porphyry deposits in the MLYB.

The distribution of trace elements in sulfides and magnetite from the Jaguar hydrothermal nickel deposit: Exploring the link with IOA and IOCG deposits within the Carajás Mineral Province, Brazil

The Jaguar nickel deposit represents an important and unconventional discovery of hydrothermal Ni resources (58.9 Mt @ 0.95% Ni) associated with magnetite and apatite within the Carajás Mineral Province, Northern Brazil. The Jaguar deposit shares several similarities with iron oxide copper–gold (IOCG) deposits of the Carajás Mineral Province, especially regarding the structural control, and the hydrothermal alteration. Although IOCG and Kiruna-type iron oxide-apatite (IOA) deposits are closely associated in several geological provinces, this association has not yet been fully constrained in the Carajás Mineral Province. The Jaguar deposit occurs near mafic–ultramafic intrusions, along a regional fault zone, and is hosted either by granitic (northern portion) or felsic subvolcanic (southern portion) rocks. It is characterized by sub-vertical zones hosting a biotite-chlorite (Bt-Chl) hydrothermal alteration with ductile structures and disseminated sulfides (pyrite and millerite) and magnetite. These zones are overprinted by sulfide-magnetite-apatite-bearing breccias, which represent the main mineralization bodies. The sulfide assemblage in the mineralized zones is dominated by pyrite, pentlandite and millerite, with minor sphalerite and chalcopyrite.We have investigated the concentration of trace elements in the magnetite and sulfides from the host rocks, different alteration facies and the mineralization at the Jaguar deposit by LA-ICP-MS. Magnetite composition ranges from higher Al, Mn, Ti and V contents, for at least part of those in host rocks (granitic and felsic subvolcanic) and Bt-Chl alteration, into lower contents in the magnetite-apatite alteration, associated with the main Ni mineralization. Magnetite with higher Ti and V contents in host rocks is associated with discrete hydrothermal alteration pockets, have high Ni/Cr ratios and plot in high temperature hydrothermal fields in multi-element diagrams. Therefore, we support that these features are compatible with a hydrothermal origin. Anomalously high-Ni contents in magnetite point that the Neoarchean mafic–ultramafic layered intrusions of the Carajás Province represent potential Ni sources for hydrothermal remobilization. Anomalously high V contents in magnetite suggest lower fO2 conditions upon the formation of the deposit. The concentration of trace elements in magnetite associated with the Jaguar deposit is similar to those from other IOCG deposits from the Carajás Province (but with higher V and Ni contents), especially the Sossego mine in the Southern Copper Belt, indicating that it could represent a Ni-rich member of the regional-scale IOCG mineral system at Carajás. Pyrite and chalcopyrite have a composition similar to those from magmatic deposits, when using previously proposed discriminant diagrams, but this is also the case for other IOA and IOCG deposits. However, low PGE contents (Ru, Rh, Ir and Os) in pyrite from the Jaguar deposit support a hydrothermal origin. Our results highlight that the classifications provided by available discriminant diagrams are not unequivocal. We suggest that multi-element diagrams represent a complementary approach to binary plots and provide a more comprehensive classification for the use of indicator minerals.

Дундговь болон Хэрлэнгийн төмрийн металлогений бүсэд тархсан төмрийн ордууд

Iron Oxide Apatite and Iron Oxide Copper Gold deposits generally consist of Fe and Cu-Au ore, and some deposits occasionally are recognized P, REE, Co, Ag and U. IOCG deposits are divided into magnetite and hematite subtypes by general ore mineral. Magnetite type IOCG has Na-Ca or, Na and potassic alteration zones, ore bodies are breccia and veins in shapes, ore-forming fluid was δ18O light supplied by magmatic and metamorphic waters. Hematite IOCG has a little potassic alteration zone, and ore bodies are formed breccia and lens in shapes in sericitic-chloritic alteration zone. Ore-forming fluid was δ18O heavy supplied by magma with a significant contribution of meteoric water. Banded Iron Formation is divided into Algoma, Superior and Rapitan sub types. The Algoma type BIF has δ18O of primary silica changed from +8‰ to +20‰ at temperatures below 100°C during diagenesis, indicating that although O isotope exchange occurs during diagenesis, low concentrations of rare earth and trace elements in siliceous shale do not change in ocean water-derived fluids. The Rapitan type, when the Earth’s oceans were almost completely covered by ice and cut off from the atmosphere, the ferruginous quartzite was deposited in the water at a time when the oceans were re-oxygenated. Prominent deposits of superior-type ferruginous quartzite occur in Paleoproterozoic sedimentary basins or in shallow-water sedimentary rocks of the continental shelf (Dartsagt, Ereen). Iron skarn deposits are divided into calcic, magnesian, and scapolite (albite) by their general chemical composition. Calcic iron skarn is developed at contact of carbonate bearing rocks and basic intrusion, and ore consists of magnetite, chalcopyrite, cobaltite, and pyrrhotite. Host rocks of magnesian iron skarn are typically dolomite, or limestone, quartzite, and schist associated with dolomitic. Ore minerals are recognized as magnetite, chalcopyrite, pyrite, sphalerite, arsenopyrite, and pyrrhotite in these type deposits (Bargilt). Host rocks are andesite, tuff, limestone, argillite at the scapolite (albite) iron skarn, then magnetite, hematite, pyrite, marcasite, chalcopyrite, sphalerite, pyrrhotite, and arsenopyrite are ore minerals.

Formation of iron oxide–apatite deposits

Formation of iron oxide–apatite deposits

Mineralization and magmatic origin of the 2.1 Ga Zhaoanzhuang magnetite-apatite deposit, North China Craton: Constraints on the formation of the Paleoproterozoic iron oxide-apatite deposits

Iron oxide-apatite (IOA) deposits provide large amounts of iron for steel industry worldwide, but their origins are still in dispute. Although IOA deposits were commonly genetically related to intermediate-mafic igneous rocks, the occurrences of IOA deposits in ultramafic rocks are scarce. The Zhaoanzhuang iron deposit in the North China Craton is characterized by comprising abundant low-Ti magnetite, apatite and ultramafic minerals (e.g., olivine, orthopyroxene), but its origin has long been controversial. These ultramafic minerals mainly occur as aggregates surrounded by magnetite in the iron ores and display typical cumulate textures and high Fo values, indicative of magmatic origin. The δ56Fe and δ18O values of magnetite from the ores range from 0.22 ± 0.03‰ to 0.32± 0.03‰ and from 2.6‰ to 4.5‰, respectively, akin to those in magmatic rocks and IOA deposits but distinct from those of metamorphic BIFs. Both types of apatite occurring in the ultramafic aggregates and the iron ores contain 2.07 to 2.69 wt% F, less than 0.65 wt% Cl, up to 7900 ppm rare earth elements (REE) and greatly variable Sr-Nd isotopic compositions, reflecting that both types are of magmatic-hydrothermal origin. The crust-like εNd(t) values (-7.1 to −5.2) of all apatite grains record reset of their Sm-Nd system, which is resulted from the involvement of carbonate fluids based on their similar REE patterns. In situ Sm-Nd isotope analyses of apatite from the ultramafic aggregates and the iron ores have yielded similar Sm-Nd isochron ages at 2100 ± 81 Ma (MSWD = 0.84) and 2096 ± 240 Ma (MSWD = 0.85), respectively, which can constrain the minimum age for the Fe mineralization. Combined with sedimentary age of the strata, the ore-forming age of the deposit was 2.3–2.1 Ga. The negative εNd(t) values of the ultramafic aggregates (-1.2 to −1.0), the iron ores (-1.8 to −1.5) and magnetite (-1.6 to −0.8) from the ores indicate that the ore-forming magma has a slightly enriched signature. Combined with linear relationship between their εNd(t) values and MgO contents, an involved mantle-derived ultramafic magma is most likely to be contaminated by the crustal material during ascending. Therefore, the Zhaoanzhuang deposit is a good Paleoproterozoic case of the rare IOA deposits associated with ultramafic magmas.

The Origin and Discrimination of High-Ti Magnetite in Magmatic-Hydrothermal Systems: Insight from Machine Learning Analysis

AbstractHigh-titanium (high-Ti, more than 1 wt % Ti) magnetite, commonly containing ilmenite exsolution, has long been attributed to an igneous origin and has been used as the most critical factor in previously developed discriminant diagrams. However, recent studies have shown that high-Ti magnetite can be present in high-temperature hydrothermal deposits, suggesting a probable hydrothermal origin. This also calls for reconsideration and necessary modification of the currently available discriminant diagrams. This high-Ti magnetite issue is particularly acute in iron oxide-apatite (IOA) deposits and raises controversy in the discussion of the origin of the high-Ti magnetite.With statistical analysis and machine learning techniques, this study applies two unsupervised dimensionality reduction methods—principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE)—on a compiled data set consisting of 876 laser ablation-inductively coupled plasma-mass spectrometry analyses of primary high-Ti magnetite from high-temperature ore-forming systems worldwide. Three models are built with different element combinations to identify magnetite of different origins. The models were further evaluated by the support vectors machine (SVM) and receiver operating characteristic (ROC) curves and proved to be able to describe the characteristics of trace element compositions of high-Ti magnetite of different origins. Our models suggest that Mg, Mn, Al, Ti, V, and Co from 59 analyzed trace elements show promising properties as effective discriminators, and on this basis, a new discrimination diagram of lg(Al) + lg(Ti) + lg(V) versus lg(Mn)/[lg(Co) + lg(Mg)] is developed for distinguishing high-Ti magnetite of igneous and hydrothermal origin. Our results also show that the high-Ti magnetite in the IOA deposits has chemical compositions similar to those of high-temperature hydrothermal deposits, including the iron oxide copper-gold and porphyry deposits, but significantly distinct from the igneous magnetite. Our study, hence, implies a magmatic-hydrothermal origin for the magnetite in IOA deposits.

Involvement of Evaporite Layers in the Formation of Iron Oxide-Apatite Ore Deposits: Examples from the Luohe Deposit in China and the El Laco Deposit in Chile

Iron oxide-apatite (IOA) deposits are important sources of iron. The role of evaporite layers in the formation of IOA ore deposits remains controversial. The Luohe deposit in eastern China and the El Laco deposit in Chile are representative IOA deposits. In this study, the S isotope characteristics of these two deposits are revisited. The formation of the Luohe ore deposit is closely related to marine evaporite layers in the Middle Triassic Dongma’anshan Formation. At Luohe, most of the sulfides and sulfates have high δ34SV-CDT values (concentrated from 6‰ to 10‰ and 16‰ to 20‰, respectively). The δ34SV-CDT values of sulfates are similar to those of marine evaporite layers (28–30‰) in the Dongma’anshan Formation. Estimates show that 46–82% of sulfur in the Luohe deposit is derived from marine evaporite layers. Unlike the Luohe deposit, the El Laco ore deposit formed in close relation to terrestrial evaporite layers from the Cretaceous-Tertiary Salta Group. At El Laco, the sulfides and sulfates have lower δ34SV-CDT values of −2.3‰ to −0.9‰ and 6.8‰ to 10.5‰, respectively. The δ34SV-CDT values of sulfates from the El Laco deposit are similar to those of sulfates from terrestrial evaporite layers (9.5‰) in the Salta Group. Estimates reveal that more than 70% of sulfur comes from terrestrial evaporite layers. These results indicate that evaporite layers have been involved in IOA ore-forming systems of both hydrothermal and magmatic deposits. Evaporite layers are proposed to have played key roles in the ore-forming processes of the Luohe and the Laco deposits and in other IOA deposits elsewhere.

Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology

The Kiruna mining district, Sweden, known for the type locality of Kiruna-type iron oxide–apatite (IOA) deposits, also hosts several Cu-mineralized deposits including iron oxide–copper–gold (IOCG), exhalative stratiform Cu-(Fe-Zn), and structurally controlled to stratabound Cu ± Au. However the relationship between the IOA and Cu-systems has not been contextualized within the regional tectonic evolution. A broader mineral systems approach is taken to assess the timing of energy drive(s) within a regional tectonic framework by conducting U-Pb zircon geochronology on intrusions from areas where Cu-mineralization is spatially proximal. Results unanimously yield U-Pb ages from the early Svecokarelian orogeny (ca. 1923–1867 Ma including age uncertainties), except one sample from the Archean basement (2698 ± 3 Ma), indicating that a distinct thermal drive from magmatic activity was prominent for the early orogenic phase. A weighted average 207Pb/206Pb age of 1877 ± 10 Ma of an iron-oxide-enriched gabbroic pluton overlaps in age with the Kiirunavaara IOA deposit and is suggested as a candidate for contributing mafic signatures to the IOA ore. The results leave the role of a late energy drive (and subsequent late Cu-mineralization and/or remobilization) ambiguous, despite evidence showing a late regional magmatic-style hydrothermal alteration is present in the district.

Magmatic-hydrothermal evolution of the El Laco iron deposit revealed by trace element geochemistry and high-resolution chemical mapping of magnetite assemblages

The Plio-Pleistocene El Laco magnetite ore bodies in the Chilean Altiplano represent an unusual subvolcanic/aerial type of an iron oxide-apatite (IOA) deposit. The textures of these magnetite ore bodies have sustained a long-standing geological controversy on the origin of iron oxide deposits with models spanning the spectrum from purely igneous to magmatic-hydrothermal processes. In particular, the link between the geochemical processes taking place in the source magma and the subsequent evolution of the overlying magmatic-hydrothermal system are still not well understood. Here we address this problem by focusing on microtextural and geochemical features of iron ore and silicate gangue minerals retrieved from drill core samples from El Laco ore bodies, as well as from the andesite volcanic host rocks. We report a comprehensive geochemical dataset of magnetite assemblages at El Laco obtained using a combination of EPMA, LA-ICP-MS, and synchrotron radiation µ-XRF methods. Microtextural and geochemical data of magnetite reveal consistent variations with depth. Magnetite in the andesitic host rocks and from deep/intermediate levels of the ore bodies have a high concentration of trace elements including Ti, V, Ni, Mn, Zn, Cr, Al, Ga, Cu and Co in comparison with magnetite from the upper sections of the ore bodies. Clinopyroxene is present in the andesite host rocks as well as the ore bodies, showing chemical differences between both types, with Mn and Fe contents that are higher in the former, and Na and Ca concentrations enriched in the latter. We interpret the enriched-to-depleted compositional trends in magnetite and clinopyroxene as resulting from a transition from purely igneous conditions to a fluid-dominated, cooling magmatic-hydrothermal system. Detailed microtextural analysis of magnetite and clinopyroxene from the ore bodies support this notion, revealing multiple growth stages punctuated by dissolution-reprecipitation processes. Our data further supports a genetic model that explains the formation of the El Laco iron oxide deposit through the injection, upward migration and venting of magmatically-derived Fe-rich fluids.

Trace element evolution of magnetite in iron oxide-apatite deposits: Case study of Daling deposit, Eastern China

In recent years, magnetite trace elements have increasingly been applied in studies into ore deposits. The magnetite trace element characteristics of different deposit types have been summarized, but to date no satisfactory explanation has been obtained as to why magnetite samples from some iron oxide-apatite (IOA) deposits exhibit similar trace element characteristics to those in iron-oxide copper gold (IOCG) deposits, or even skarn deposits. The Daling IOA deposit is located in the Luzong volcanic basin, Eastern China. Multi-stage magnetite have developed within the deposit; which provides a good opportunity to study the evolution process of magnetite trace elements in an IOA deposit. Here, sensitive high-resolution ion microprobe (SHRIMP) in situ sulfur isotope analysis was carried out for pyrites at different depths in the deposit. Pyrites at different locations exhibited similar sulfur isotope compositions, falling within the magmatic sulfur range (0.1‰–5.2‰), indicating that the ore-forming fluid of the Daling deposit was not affected by the Triassic evaporite, and that the trace element characteristics of its magnetite were mainly controlled by its magmatic-hydrothermal evolution process. Magnetite within the deposit can be divided into three sub-stages. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis revealed that magnetite (Mag-a) in vertical veinlets exhibits the highest Ti, V, Mn, and Zn contents; magnetite (Mag-b), which is associated with diopside and tremolite in coarse veinlets, exhibits the highest Mg, Al, Co, and Ni contents and brecciated magnetite (Mag-c) exhibits the lowest V content, the highest Mn and Zn contents, and similar Mg, Al, Ti, and Co contents to those of Mag-b. Comparing the trace elements of the three types of magnetite revealed that hydrothermal fluid can assimilate and absorb albite-diopside altered rock that forms in the early stage, resulting in hydrothermal fluid that is rich in Mg, Al and Si. Thus, magnetite samples in IOA deposits can exhibit similar features to those in skarn deposits through multi-stage, long-distance fluid evolution. Therefore, before using magnetite trace elements to discuss the characteristics of hydrothermal fluid, it is important to carefully investigate the basic geological characteristics of a given deposit and the mineralogical characteristics of its magnetite.

U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden

To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit approximately 1 km northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon concordia age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite sitting on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated with the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields seven analyses (<1.5 % relative discordance which included six common Pb-corrected analyses and one analysis where no significant common Pb was detected) that yield a 207Pb/206Pb weighted average age of 1889 ± 26 Ma that we interpret as the most probable minimum age of fault initiation. The overlap in age of the host volcanic rock and the fault implies that during basin development, contemporaneous volcanism and syn-volcanic faults may have played an important role during iron ore emplacement. A U-Pb lower intercept age of apatite from the Nukutus iron oxide-apatite deposit provides a first indication that the area was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma. Further temporal constraints on exhumation and basin inversion is given by syn-tectonic titanite along a brittle-ductile reverse shear zone to the east of the study area that shows limited presence of significant common Pb and is part of a sodic-calcic + Fe + Cl hydrothermal alteration assemblage. Titanite grains that show a well-developed zonation yield a U-Pb concordia age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Titanite grains from the same sample that show less pronounced zonation yield a U-Pb concordia age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.

Formation and evolution of Th–REE mineralizing fluids at the Kiruna‐type Choghart iron oxide–apatite deposit, Central Iran: Insights from fluid inclusions and H‐C‐O isotopes

The Choghart iron oxide–apatite (IOA) deposit is one of the largest iron mines of the Bafq district in Central Iran. This deposit is hosted by the Early Cambrian rhyolites, and diabase dikes crosscut both host rocks and the ore bodies. The Choghart rhyolites erupted in a continental arc setting, while the Choghart diabase dikes formed in a back‐arc basin environment. Thorite, minor titanite, and REE‐oxide are the main hosts of Th and REEs. The mineralogy and geochemistry support that the Th–REE mineralization formed at relatively reduced conditions. The presence of calcite accompanied by thorite and titanite suggests that Th and REE probably migrated as carbonate complexes in the mineralizing hydrothermal fluids. Microthermometric data of calcite associated with thorite indicate that the salinity of the ore‐forming fluids varies from 20 to 30 wt% NaCl equivalent with temperature estimates between 300 and 370°C. The narrow range of homogenization temperature and low salinities of the fluid inclusions imply the presence of only one fluid phase in the Th–REE mineralization. The calcite δ13CPDB (−3.9 to −4.1‰) and δ18OSMOW (6.6–7.0‰) support a magmatic source for the ore‐forming fluids. Actinolite δD (5.55–6.72‰) and δ18O (−100.8 to −82.4‰) also suggest a magmatic source of the ore‐forming fluids. Microthermometric data imply that fluid–rock interaction and cooling were critical factors triggering the thorite precipitation at Choghart IOA deposit. Stable isotopic data indicate that post‐magmatic fluids derived from rhyolitic magmas played a significant role in the Th–REE mineralization.

Process Mineralogical Assessment of the Grinding Products of the Per Geijer Iron Oxide-Apatite Deposits

ABSTRACT Information obtained from comminution test work at the laboratory scale can be utilized to characterize ore types and predict their behavior during comminution at the industrial scale. Comminution tests with a laboratory-scale rod and ball mill of 13 predefined ore types from the Per Geijer iron oxide-apatite deposits were conducted. The grinding setup refers to the so-called Malmberget method used at LKAB, characterized by a subsequent circuit of rod and ball mill grinding. The highest P80 values were obtained by grinding only in the rod mill for 10 min (step A). Ball mill grinding for 25 min (step B) and 35 min (step C) gave a very narrow range of P80 values. Hematite-dominated ore types had significantly higher P80 values after the primary grinding step A compared to the other ore types. Generally, Fe content increased in finer particle size classes while CaO and P contents decreased. The influence of silicates or phosphates is dependent on the dominant iron oxide. Magnetite-dominated ore types are more likely to be affected in their comminution behavior by the presence of silicate minerals. In contrast, hematite-dominant ore types are instead influenced by the presence of apatite. The difference in the degree of liberation of magnetite and hematite between ore types depends on size fractions rather than the amount of gangue in the ore most likely caused by very fine intergrowth of both iron oxides. A consolidation from 13 to 8 ore types is favored, supporting possible future mining of the Per Geijer deposits.

Formation of the Chah-Gaz iron oxide-apatite ore (IOA) deposit, Bafq District, Iran: Constraints from halogens, trace element concentrations, and Sr-Nd isotopes of fluorapatite

The textures, chemistry and Sr-Nd isotopic compositions of apatite from the Chah-Gaz iron-oxide apatite (IOA) deposit in the Bafq metallogenic belt, central Iran, were studied to investigate the formation of this ore deposit. Two generations of apatite were recognized based on Cl/F and Cl/OH ratios. Primary fluorapatite, which is coeval with magnetite in the massive ore bodies, is chemically homogeneous and characterized by Cl/F < 0.05 and Cl/OH in the range of 0.01–0.07. By contrast, F-depleted apatite rims are present in apatite hosted in veinlets that crosscut the massive ore bodies and are disseminated in the igneous host rocks, and have Cl/F and Cl/OH-apatite ratios of 0.08–0.12 and 0.15–0.79, respectively. The F-depleted rims are also depleted in LREEs, Th and U, consistent with the presence of secondary monazite, xenotime and thorite that formed by coupled dissolution-reprecipitation. The whole-rock Nd–Sr isotopic data ((87Sr/86Sr)(I) = 0.7052 to 0.7064 and ɛNd(t) = +1.3 to + 2.7) of gabbro-diorite indicate an mantle source, while the high -K, calc-alkaline-shoshonitic volcanic host rocks have εNd(t) = − 5.5 to − 7.6, clearly reflecting mixing between mantle-derived mafic magmas and assimilated Proterozoic basement. The initial 87Sr/86Sr ratios and ɛNd values of both F-rich and -depleted apatites (0.7038 to 0.7050 and −0.3 to + 6.5, respectively) are similar to gabbroic rocks and support a magmatic source for primary fluorapatite, with minimal or no crustal contribution, and indicate that the magmatic event with negative ɛNd values did not affect the whole-rock Sm-Nd signature of the ore. Petrography plus geochemical and Nd-Sr isotopic data of both studied fluorapatite, which come from iron oxide stage, are consistent with a combined igneous/magmatic-hydrothermal genesis for the Chah-Gaz IOA deposit, with low degrees of hydrothermal overprint, as evidenced by the formation of F-depleted (Cl-rich) apatite rims. The relatively constant Sr-Nd data in apatite are consistent with superimposed, episodic hydrothermal fluids from the same, evolving, magmatic-hydrothermal system.

Textures and chemical compositions of the Narm iron oxide-apatite deposit in Kuh-e-Sarhangi District (Central Iran): Insights into the magmatic-hydrothermal mineralization

The Narm deposit is located in the Kuh-e-Sarhangi district which is a main part of the most significant Iranian iron mineralization belt, the Kashmar-Kerman Tectonic Zone (KKTZ) in Central Iran. The Narm deposit comprises an estimated total of ∼ 135000 tons of iron ore with an average grade of ∼ 55% Fe and is hosted in Early Cambrian volcano sedimentary rocks of the Rizu formation. Ore occurrences in this deposit consist of lens-shaped magnetite ore bodies, magnetite-apatite-actinolite veins and locally rare brecciated dolomite with magnetite clasts. Magnetite, pyrite, chalcopyrite and specularite associated with apatite, actinolite, biotite and carbonate minerals form the primary main mineral assemblage which is accompanied by hematite and goethite as the secondary minerals. Magnetite as the most current mineral of Narm deposit reveal the magmatic to hydrothermal evolution of mineralization. Magmatic magnetite minerals (Mag I) are dark-gray inclusion-rich magnetite spatially correlated with high temperature Ca-Fe alteration. The brighter inclusion-free hydrothermal magnetite groups (Mag II and Mag III) form during the temperature decreasing of the mineralizing fluid. According to the magnetite chemistry examination, most magnetite fall into the field for magnetite from iron-oxide apatite (IOA) deposits. Apatite minerals with F/Cl > 2, belong geochemically to the fluorapatite type. In addition to the primary dolomite, there are some hydrothermal Fe-rich dolomites and Mn bearing ones, indicating the hydrothermal fluid playing the important role for Fe-rich mineralization. In respect to fluid evolution, fluid inclusion analysis of calcite and apatite minerals form the magnetite paragenesis assemblage represent homogenization temperature range for fluid between 325 and 557℃. The salinity of fluid varied from 7.7 to 11.6 wt% NaCl equivalent and a cooling trend with the dominant chlorine complex as an agent for deposition of the Fe-rich ores. The geochemical characteristics of the δ18Ofluid values of magnetite (from + 6.1 to + 10.4‰) and δ18Ofluid values of actinolite (from + 7.7 to + 12.5‰) represent the magmatic-hydrothermal (δ18Ofluid > + 0.9 ‰) formation process. The iron rich Al-clinochlore composition from the alteration zone indicates a temperature range between 250 and 330℃ which points to a temperature reduction of hydrothermal fluids in this mineralizing zone. The integrated geochemical data from this investigation, including mineral chemistry, microthermometry of fluid inclusions and oxygen isotope data all reveal a magmatic-hydrothermal genesis for this deposit.

Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides

AbstractTo guide future exploration, this predominantly field based study has investigated the structural evolution of the central Kiruna area, the type locality for iron oxide-apatite deposits that stands for a significant amount of the European iron ore production. Using a combination of geologic mapping focusing on structures and stratigraphy, petrography with focus on microstructures, X-ray computed tomography imaging of sulfide-structure relationships, and structural 2D-forward modeling, a structural framework is provided including spatial-temporal relationships between iron oxide-apatite emplacement, subeconomic Fe and Cu sulfide mineralization, and deformation. These relationships are important to constrain as a guidance for exploration in iron oxide-apatite and iron oxide copper-gold prospective terrains and may help to understand the genesis of these deposit types. Results suggest that the iron oxide-apatite deposits were emplaced in an intracontinental back-arc basin, and they formed precrustal shortening under shallow crustal conditions. Subsequent east-west crustal shortening under greenschist facies metamorphism inverted the basin along steep to moderately steep E-dipping structures, often subparallel with bedding and lithological contacts, with reverse, oblique to dip-slip, east-block-up sense of shears. Fe and Cu sulfides associated with Fe oxides are hosted by structures formed during the basin inversion and are spatially related to the iron oxide-apatite deposits but formed in fundamentally different structural settings and are separated in time. The inverted basin was gently refolded and later affected by hydraulic fracturing, which represent the last recorded deformation-hydrothermal events affecting the crustal architecture of central Kiruna.