Economic Geology最新文献

{"title":"Syn- and Postdepositional Controls on the Composition of Pyrite and Pyrrhotite in the Windy Craggy Cu-Co Volcanogenic Massive Sulfide Deposit, British Columbia, Canada","authors":"Tarryn K. Cawood, Jan M. Peter, Duane C. Petts, Matthew J. Polivchuk","doi":"10.5382/econgeo.5181","DOIUrl":"https://doi.org/10.5382/econgeo.5181","url":null,"abstract":"Pyrite and pyrrhotite from the Windy Craggy volcanogenic massive sulfide (VMS) deposit, British Columbia, Canada, were investigated using combined in situ compositional mapping (by laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS]) and microstructural mapping (by electron backscatter diffraction [EBSD]) to elucidate how their compositions were affected by hydrothermal processes and subsequent deformation and metamorphism. Early pyrite was precipitated rapidly from cool (<250°C) hydrothermal fluids with a significant seawater component and incorporated substantial quantities of a wide variety of trace elements, including the low-temperature suite As-Ag-Sb-Au-Tl-Pb. As the hydrothermal system evolved, this early pyrite was overgrown during subseafloor zone refining and replaced by massive pyrrhotite-chalcopyrite-pyrite mineralization containing Co-Ni-Cu-Se-Mo-Bi, under high-temperature (~350°–380°C), reducing conditions. During deformation and metamorphism at greenschist facies conditions (≥370°C), pyrrhotite was mechanically remobilized by dislocation creep and dynamic recrystallization, expelling elements hosted in mineral inclusions (Cu, Mo, Ag, Sb, Pb, and Bi) but largely retaining direct, stoichiometric substitution elements (Co, Ni, and Se). Pyrite is more competent than pyrrhotite, but local dynamic recrystallization did occur and similarly expelled most elements incorporated by coupled substitution or in inclusions (Cu, Zn, Mo, Ag, Sn, Sb, some Te, Au, Tl, Pb, and Bi), while retaining direct substitution elements (Co, As, Se, and some Te). Synmetamorphic phases, like pyrite overgrowths and minor cobaltite, are distinctly Co and As rich. Within the Windy Craggy deposit, significant variations exist in pyrite and pyrrhotite trace element compositions, reflecting both syn- and postdepositional processes. In general, low-temperature elements are present in sulfide mineral inclusions or as coupled substitutions and may be positive indicators of proximity to hydrothermal mineralization, but they are readily remobilized during hydrothermal, metamorphic, or deformational sulfide modifications. Several high-temperature elements are incorporated tightly into the crystal lattice of pyrite and pyrrhotite and are thus better retained through such modifications.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"115 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145203131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fertility Assessment of Tectono-Magmatic Cycles in the Tres Cerrillos Prospect (Western Cordillera of Ecuador)","authors":"Hugo Carrasco, Massimo Chiaradia, Kalin Kouzmanov, Alexey Ulianov, Richard Spikings, Carlos Urrutia, Sergio Cubelli, Carolina Rodríguez, Angelo Aguilar, Juan Jaramillo, Hugo Narvaez, Yorki Patiño, Sergio Pichott","doi":"10.5382/econgeo.5180","DOIUrl":"https://doi.org/10.5382/econgeo.5180","url":null,"abstract":"This study explores the mineralizing potential and the magmatic controls of Miocene-Pliocene magmas in the Western Cordillera of Ecuador, evaluating the temporal evolution and petrogenesis of magmas associated with multiple porphyry Cu systems at the Tres Cerrillos prospect. Within the prospect, four distinct magmatic cycles at ~11, ~10.6, ~8.7, and ~2.7 Ma were identified, spanning the mid-Miocene to Pliocene. Petrographic, geochemical, and geochronological data reveal a transition from barren to fertile behavior within each cycle, marked by ramp-ups in key geochemical fertility proxies (Sr/Y, V/Sc, La/Yb, Dy/Yb, Zr/Y, and (EuN/Eu*)/YbN). These fertile magmatic signatures are associated with magmas evolving at high-pressure and high-H2O conditions in the lower crust, leading to amphibole and garnet fractionation. Assimilation-fractional crystallization modeling of rare-earth elements indicates a high degree of assimilation of the oceanic Pallatanga basement during the evolution of the Tres Cerrillos magmas. All magmatic cycles have a duration of ~0.5 Ma; however, potentially longer ramp-up periods in fertility proxies, evidenced by inherited zircons and 40Ar/39Ar geochronology, place the Cielito and El Pantanal targets as the most prospective at Tres Cerrillos. A long-lived ramp-up of fertility indicators is considered a hallmark of supergiant porphyry copper deposits. Exhumation phases (~15–13, ~10–9, and ~6–5 Ma) related to periods of increased compression in Ecuador precede the onset of the magmatic cycles. These compressional phases could have favored magma storage and differentiation at deep crustal levels before magmas were transferred to upper crustal reservoirs under more neutral stress conditions. The transition from a compressional to a more neutral tectonic stress regime could have been modulated by the oblique subduction of the topographically irregular Carnegie Ridge beneath the Ecuadorian continental margin, which highlights the importance of subduction dynamics in the formation of porphyry copper deposits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"37 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145203133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Interpretation of Pyrite Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Maps Using Machine Learning: A Case Study of the Colosseum Au Deposit, Southern California","authors":"Nelson Román, Daniel D. Gregory, Simon E. Jackson, Jean-Luc Pilote, Duane C. Petts","doi":"10.5382/econgeo.5172","DOIUrl":"https://doi.org/10.5382/econgeo.5172","url":null,"abstract":"This study explores the application of machine learning techniques for an enhanced interpretation of pyrite laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) maps. The Colosseum Au deposit, in southern California, was considered as a case study. Colosseum is genetically related to a rhyolitic breccia-pipe complex, where Au mineralization is associated with two main pyrite generations—early pyrite and late pyrite. Our machine learning workflow involves the detection of distinct compositional zones in individual maps through unsupervised clustering, and a second clustering step where these zones are grouped by compositional similarity, enabling the direct comparison between different maps and providing a compositional overview of pyrite representative of the various styles of mineralization present in the deposit. Clustering of individual maps correctly differentiated between distinct growth zones in early pyrite, fractures that crosscut early pyrite growth, and zones of late pyrite growth, matching petrographic observation. All the zones detected by this first step, in turn, were classified into two compositionally distinct groups and a third transitional group, enabling the direct comparison between maps while keeping petrographic consistency. For Colosseum, our approach revealed that (1) Au is more abundant in late pyrite than early pyrite, but significant amounts can be found in both generations and in both Colosseum mineralized breccia pipes; (2) the transition from early to late pyrite is represented by a change from a Co-Ni-Te–rich end member to a Cu-Ag-Zn-Sb-Tl–rich end member; and (3) Au is directly correlated with As in both pyrite generations.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"17 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145181124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Volcano-Sedimentary Lithium Occurrences in Barstow, California, and Their Related Formation Mechanisms Determined by Stable Isotope Analyses of Carbonates and Clays","authors":"Catherine A. Gagnon, Kristina L. Butler, Kevin Robertson, Christopher Emproto, Phil Gans, Ryan Eden, Daniel E. Ibarra, Thomas R. Benson","doi":"10.5382/econgeo.5174","DOIUrl":"https://doi.org/10.5382/econgeo.5174","url":null,"abstract":"The production of lithium (Li) from underexplored volcano-sedimentary Li deposits could increase the Li stockpile for the future while diversifying the available sources of Li needed for the energy transition. Here, we investigate the occurrence, distribution, and potential enrichment mechanisms for recently discovered Li-rich mudstones within the Miocene Barstow Formation in the Mojave Desert of California. Bulk mudstone Li concentrations from the Barstow Formation range from 20 to 2,500 ppm, and the most enriched samples correspond to a greater proportion of smectite relative to illite, chlorite, and kaolinite. The Li-enriched mudstones tend to contain analcime, calcite, dolomite, and feldspar. Bulk mudstone Li concentrations covary with the oxygen isotope composition of the carbonate phases (δ18Ocarb; 17–35‰ Vienna standard mean ocean water). Smectite δ18O values mirror paired carbonate trends and contain an evaporitic slope in δ18O-δD space, suggesting both minerals formed from the same evaporatively enriched evolving water reservoir. Calculated smectite formation temperatures range from 17° to 51°C and carbonate clumped isotope formation temperatures range from 15° to 50°C, suggesting low-temperature processes drive Li enrichment. The combined geochemical and stable isotope results suggest that between 19 and 13 Ma, evaporation of ephemeral underfilled to perennial balance-filled lake waters led to the Li enrichment of pore waters and subsequent Li smectite authigenesis. We speculate the primary source of Li to ancient lake/pore waters came from the weathering of glassy volcanic ash shards to the lake and aqueous Li weathered from coeval felsic volcanic rocks in and around the Barstow basin. Evidence for Li-rich hydrothermal contributions to lake/pore waters is minor. Our study suggests that other deposits set in nearby extensional regimes may have had similar paleoenvironmental controls surrounding the formation of authigenic, Li-rich smectite.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"36 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineral-Textural Characteristics of Lithium Pegmatite Ores of Western Australia","authors":"Martin A. Wells, Mark G. Aylmore, Brent I.A. McInnes, William D.A. Rickard, Kai Rankenburg","doi":"10.5382/econgeo.5176","DOIUrl":"https://doi.org/10.5382/econgeo.5176","url":null,"abstract":"Mineralogical and geochemical characterization of some of the main lithium-cesium-tantalum (LCT) pegmatite intrusions of the Archaean Yilgarn and Pilbara cratons, Western Australia, was undertaken to establish the key parameters that distinguish these important Li-ion battery resources. The majority of Western Australia pegmatites investigated belong to one of three main complex subtypes: (1) spodumene—Greenbushes, Kathleen Valley, Dome North, Mount Marion; (2) petalite—Londonderry, Dome North; and (3) lepidolite—Sinclair cesium. Examples of less common pegmatite types included Mount Cattlin, Bald Hill, and Pilgangoora (albite-spodumene type) and the Dalgaranga pegmatite (albite type). Spodumene shows a near-stoichiometric LiAlSi2O6 composition with a Li2O content of ~8.0 wt %. Impurities of commercial importance, Fe (+ Mn) varied up to 1 to 1.2 wt % with Na (500–1,200 ppm), as the only other trace element of significance detected in spodumene. Structural deficiencies of Li on the M2 site in the pyroxene structure contribute to the susceptibility of spodumene to alteration and to the preferential removal of Li, relative to Al and Si, during postcrystallization, and hydrous alteration resulting in reduced Li contents of 5.50 to 5.84 wt % Li2O. Spodumene is universally affected by two key types of alteration: a less common, postcrystallization, pseudomorphic replacement of spodumene by a massive, dark-green-to-black, fine-grained, Li-bearing mica-chlorite (cookeite) assemblage (Mount Cattlin and Bald Hill pegmatites); and a more widespread alteration characterized by symplectitic assemblages of graphic-textured, spodumene-quartz intergrowth (SQUI) along the crystal margins of spodumene in contact with Na/K-feldspar. Related to the former alteration style is a pervasive, secondary sericite-like vein alteration, developed along internal fractures and cleavage planes of spodumene. In all cases, alteration leads to the loss of Li from spodumene, and, in relation to the pseudomorphic replacement and vein alteration, introduces significant K and lesser trace element impurities such as F, Mn, Fe, Mg, and Rb. Mineral-textural associations revealed a more coarsely textured but unrelated SQUI developed in the upper petalite zone at the Dome North deposit and in the Li zone in the Greenbushes pegmatite formed by the decomposition of precursive petalite (confirmed) and virgilite (inferred), respectively. Changes in mica (muscovite and lepidolite) composition followed well-correlated trends with Li wt % positively correlated with F wt % and Al/Si negatively correlated with the Li content. The K, Rb, and Cs composition systematics of mica in Western Australia and worldwide pegmatites indicate a complex fractionation mechanism than cannot be explained alone by simple Rayleigh fractionation, which may operate during pegmatite crystallization. A new zircon U-Pb age of 2631 ± 4 Ma for the Greenbushes pegmatite is older than the previously determined age 2527 Ma and ","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"58 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Using Machine Learning to Characterize the Genesis of Lithium-Bearing Sedimentary Rocks in the Western United States","authors":"Rachel Hampton, Thomas R. Benson","doi":"10.5382/econgeo.5158","DOIUrl":"https://doi.org/10.5382/econgeo.5158","url":null,"abstract":"The lithium used in batteries is currently sourced exclusively from high-altitude saline brines and pegmatites in orogenic metamorphic belts. In the coming years, lithium-bearing volcano-sedimentary deposits are expected to become an increasingly important source of lithium, with several volcano-sedimentary deposits under varying stages of development throughout the Basin and Range province (United States and Mexico) and Serbia. Foremost among these is the Thacker Pass project hosted in lacustrine moat sediments of the ~16.3 Ma McDermitt caldera, Nevada, United States. Because this type of deposit is critical to obtaining a secure domestic supply of lithium in the United States, we initiated a study on more than 50 basins in 21 states. Through observational field work, detailed sampling, and geochemical analyses on the stratigraphic sequences of interest, we created a database of over 1,500 samples characterizing sedimentary basins in the western United States to ascertain the occurrences and formation of volcano-sedimentary lithium deposits. We use multinomial logistic regression and principal component analysis in addition to basic statistical analysis to create a predictive model for lithium concentration utilizing key features of each basin. Basins containing economic (>1,000 ppm) lithium are predominantly characterized by Miocene-aged, small (<1,500 km2) closed lacustrine systems, with volcanic input, containing fine-grained clay material, often deposited under reducing conditions. The model can be used to predict the concentration of lithium in sedimentary databases without lithium data and can be applied as a modern tool for volcano-sedimentary lithium deposit exploration in basins globally.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"90 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145127625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Are Alkalic Porphyry Deposits Overlain by Advanced Argillic Lithocaps?","authors":"Richard H. Sillitoe, Jeffrey W. Hedenquist","doi":"10.5382/econgeo.5179","DOIUrl":"https://doi.org/10.5382/econgeo.5179","url":null,"abstract":"A commonly highlighted feature that distinguishes alkalic porphyry deposits from those associated with calc-alkaline magmatism is a paucity of the advanced argillic alteration that can form shallow-level lithocaps. This scarcity has been attributed to either the inability of alkalic systems to generate the necessary hyperacidic fluids or erosional removal. Here, it is concluded that erosional removal is responsible, as supported by the following four lines of evidence: Alkaline stratovolcanoes at convergent margins emit as much SO2—the principal ingredient for hyperacidic fluid formation—as those in calc-alkaline arcs;At least one example of recently formed lithocap alteration in an alkaline volcano (Vulcano, Italy) is known;Remnants of advanced argillic lithocaps are present in several alkalic porphyry systems, but only those of Cenozoic age, whereas Paleozoic and Mesozoic deposits, including those in the Macquarie arc of New South Wales, Australia, and the Intermontane belt of British Columbia, Canada, appear to lack them; andAvailable fluid inclusion pressure estimates for alkalic porphyry deposits show paleodepths of at least 1.5 km, possibly up to several km, for deposits lacking lithocaps, consistent with their erosional removal. Therefore, it is concluded that preservation potential, influenced to a significant degree by formational age, is a fundamental control on the presence or absence of lithocaps above alkalic porphyry deposits—as, of course, it is in porphyry systems hosted by calc-alkaline intrusions. Thus, the presence of lithocaps in association with both alkaline and calc-alkaline igneous centers is evidence for concealed shallow intrusions and potential porphyry-type mineralization.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"115 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145035672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soil Geochemistry Toward Lithium Pegmatite Exploration: Building a Machine-Learning Predictive Algorithm via Portable X-Ray Fluorescence","authors":"Luiza Maria Pereira Pierangeli, Mona-Liza C. Sirbescu, Sérgio Henrique Godinho Silva, David C. Weindorf, Thomas R. Benson, Nilton Curi","doi":"10.5382/econgeo.5166","DOIUrl":"https://doi.org/10.5382/econgeo.5166","url":null,"abstract":"As demand for lithium (Li) increases, cheaper, more sustainable, and faster methods are needed for the identification and characterization of new Li deposits. Lithium-rich pegmatites are major sources of Li, but their exploration is often hindered by soil cover. Portable X-ray fluorescence (pXRF) can rapidly and accurately quantify soil chemistry to determine the bedrock economic potential, but unfortunately, Li is undetectable via pXRF. Herein, pXRF data and random forest models were used to predict both Li contents in soil samples and Li-rich soil parent material based on abundances of 15 predictors (K, Rb, Al, Ba, Ca, etc.). For comparison, support vector regression and neural network deep learning were also conducted. The data set consisted of 112 soil samples collected over spodumene-rich pegmatites, barren granitic pegmatites, peraluminous granite, and metamorphic host rocks from forested, glaciated northern Wisconsin and Michigan, United States. Lithium abundances were independently measured using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The best Li prediction was achieved using neural networks, yielding a coefficient of determination (R2) of 0.90, a root mean square error (RMSE) of ~40 mg × kg–1, and residual prediction deviation of 3.2. The best parent material prediction model was achieved using random forest, with an overall accuracy of 0.88. Portable XRF analysis discriminates among soil samples formed on bedrock with distinct mineralogy. Using pXRF combined with appropriate machine learning models to predict the Li contents in the soil and the type of underlying bedrock could become an alternative, more efficient, and less invasive exploration method compared to traditional trenching.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"42 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144930952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithium in the Eastern Brazilian Pegmatite Province: A Synthesis Highlighting Spodumene-Rich Deposits","authors":"Antônio Carlos Pedrosa-Soares, Hélio Botelho Diniz, Carlos Henrique Cravo Costa, Anderson Victoria, André Guimarães, Fabiana Guimarães, Gilberto Silva, Laura Wisniowski, Paula Serrano","doi":"10.5382/econgeo.5175","DOIUrl":"https://doi.org/10.5382/econgeo.5175","url":null,"abstract":"Covering 150,000 km2, the Eastern Brazilian pegmatite province stands out as one of the largest populations of rare element pegmatites in the world. The province is a result of metamorphic-magmatic processes that produced enormous volumes of distinct granite types and countless pegmatites in the Ediacaran-Cambrian Araçuaí orogen. Among the 12 pegmatite districts of the Eastern Brazilian pegmatite province, only three contain spodumene-bearing pegmatites, and only one contains spodumene-rich deposits that may reach tens of million tons of lithium ore. This is the Araçuaí district, which accounts for most of the lithium ore produced in Brazil and all recent discoveries of spodumene-rich deposits, reaching over half a billion tons of lithium ore resources. This world-class lithium district comprises distinct spodumene-bearing deposits named, for prospecting purposes, spodumene-rich pegmatites (SRP), spodumene-petalite pegmatites (SPP), spodumene-perthite pegmatites (PSP), perthite-tourmaline pegmatites (PTP), and albite-tourmaline pegmatites (ATP). All these pegmatites postdate the regional tectono-metamorphic events and are found close (1–5 km) to intrusions comprising two-mica, muscovite-albite, and pegmatoid leucogranites. Low-pressure/high-temperature metasedimentary successions with cordierite-biotite (± andalusite) schists host the SRP, SPP, and PSP deposits. They contain spodumene disseminated in unzoned to poorly zoned pegmatites that form dike swarms or large single bodies or in spodumene-rich units of simple zoned pegmatites. The PTP and ATP deposits are relatively poor in spodumene, which is found in internal zones, quartz cores, and/or albite-rich units of complex zoned pegmatites. Field mapping, soil geochemistry, trenching, and intensive drilling revealed the large Bandeira spodumene deposit in just 2 years, which is described here as an example of highly successful, knowledgedriven exploration work.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"112 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144930954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Structural Setting and Controls of Giant Lithium Pegmatite Deposits in the Archean Pilbara Craton, Western Australia","authors":"John L. Grigson, Mike W. Grigson, Anthony I.S. Kemp, Steffen G. Hagemann, Marcus T. Sweetapple","doi":"10.5382/econgeo.5170","DOIUrl":"https://doi.org/10.5382/econgeo.5170","url":null,"abstract":"The giant lithium pegmatite deposits of the Archean Pilbara craton in Western Australia are located within the Turner River district, where they are associated with D4 structures and granitic intrusions of the Split Rock Supersuite, all of which are an expression of the final phase of orogenic activity in the granite-greenstone nucleus of the craton between 2.89 and 2.82 Ga. Progression of the D4 orogenic event involved early D4a wrench faulting, followed by emplacement of the granitic intrusions, and finally onset of D4b ductile shear zone deformation and the formation of the lithium pegmatite deposits. The giant deposits at Pilgangoora and Wodgina comprise vertically stacked sets of lithium pegmatite intrusions that were emplaced episodically during ductile fracturing, at lower amphibolite facies, within strained supracrustal wall rocks in D4b shear zones. Closely spaced D4a oblique faults are a feature of the deposit settings and, although they are an expression of earlier brittle deformation, an important role is recognized for these structures as passive attractors of coaxial strain during D4b shear zone deformation. The coaxial strain manifested as constriction and vertical extrusion in the deposit settings, and this is unique within the broader D4b shear zone array, which mostly expresses noncoaxial strain in the form of oblique extrusion. Together, the partitions of vertical and oblique extrusion are considered the product of regional transpression. Migration of low-viscosity melts that formed the lithium pegmatite intrusions was clearly favored within the partitions of D4b coaxial strain. This is attributed to the faster rates at which coaxial strains accumulate, which enhanced the potential for melt migration and intrusion emplacement, most likely through a combination of intergranular percolation and ductile fracturing. The convergence of D4a faults and D4b shear zones, as well as the association of such with lithium pegmatite intrusions, is an important criterium for exploration targeting. The structural disruption arising from D4a faults is perhaps the most distinctive feature expressed in satellite and airborne magnetic images, and therefore mapping, sampling, and/or drilling should focus within regions of overlap between shear zones and fault disruption.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"84 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144919379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}