Dual and Multi Energy XRT and CT Analyses Applied to Copper-Molybdenum Mineralizations in Porphyry Deposits

X-ray transmission (XRT) and computed tomography (CT) was used on five samples from the Niaz porphyry Cu–Mo deposit in Iran, representing different alteration zones. Analysis of three-dimensional CT data revealed structural information and groups of elements with low, medium and high attenuation, which were assigned to minerals previously determined by scanning electron microscopy. Thus, the mineralization can be located, and the metal/waste ratio can be estimated, leading to more precise ore body modelling and process parameter determination. CT is useful for selected samples as it is time consuming. XRT can be used as real-time process on conveyor belts.

Apatite fingerprints on the magmatic-hydrothermal evolution of the Daheishan giant porphyry Mo deposit, NE China

Porphyry deposits are the main source for global Cu and Mo production. The generation of hydrous silicate magmas and subsequent separation of volatile-rich magmatic fluids with hydrothermal alteration are significant processes leading to the formation of porphyry deposits. However, a specific understanding of these processes has been limited by a lack of direct mineralogical records in the evolving magmatic-hydrothermal system. In this paper, we present an integrated textural and geochemical investigation on apatite from the giant Daheishan porphyry Mo deposit in NE China, illustrating that apatite can be a potential recorder of the magmatic-hydrothermal evolution of porphyry systems. Apatite from the ore-forming porphyry displays distinctive core-rim textures, with melt inclusions in the resorption cores (Type-A1) and co-existing of melt and fluid inclusions in the euhedral rims (Type-A2), indicating a magmatic-hydrothermal origin of apatite. This is also supported by both chemical and isotopic compositions obtained by in situ analyses using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) and LA-multi collector-ICP-MS. The late Type-A2 apatite is relatively enriched in incompatible elements, such as rare earth elements (REE) and Th, but slightly depleted in fluid-mobile elements such as Na and S, compared to the early Type-A1 apatite. Relatively homogeneous (87Sr/86Sr)i ratios (0.70436−0.70504) of the Type-A1 and Type-A2 apatites indicate that they were formed in a relatively closed system without detectable contamination. Meanwhile, some apatite in the wall rock (biotite granodiorite) shows characteristics of secondary altered textures, resulting from the intensive alteration by hydrothermal fluids exsolved from the porphyry system. Apatite trapped in mineral phenocrysts of the wall rock is usually unaltered (Type-B1 apatite), with clear oscillatory growth zones in cathodoluminescence (CL) images. In contrast, the intergranular apatite is commonly altered (Type-B2 apatite), with chaotic zoning in CL images, abundant micro-fractures and secondary fluid inclusions. Compositionally, the Type-B2 apatite shows notable tetrad REE patterns, relatively lower light-REE and S contents, and elevated 147Sm/144Nd ratios compared to the Type-B1 apatite. LA-ICP-MS U-Pb dating yields a lower intercept age of 171.4 ± 2.3 Ma for Type-B2, which is consistent with the age of 171.5 ± 2.4 Ma for Type-A2, but is notably younger than the Type-B1 apatite (175.5 ± 1.3 Ma). It is suggested that the Type-B2 apatite has been significantly reset by hydrothermal fluids exsolved from the porphyry system. Therefore, we conclude that the textures and geochemistry of apatite in porphyry systems can be used as a potential proxy for recording fluid exsolution and hydrothermal alteration processes.

Ore-magmatic systems of the copper-porphyry type of the Greater Caucasus

Статья посвящена выявлению особенностей геологического строения и минерагении Танадон-Сангутидон-Казбекского района проявлений медно-порфировых минерализаций Центральной части Большого Кавказа и оценке соответствия геологических обстановок оруденения современным моделям рудно-магматических систем медно-порфирового типа. Актуальность работы определяется необходимостью разработки научно-методической основы прогнозирования и поисков скрытого оруденения. Цель исследования.Выявить особенности геологии и минерагении Танадон-Сангутидон-Казбекского рудного района и установить соответствие обстановок оруденения современным моделям рудно-магматических систем медно-порфирового типа. Методы. Сравнительно-геологический и металлогенический анализ на основе современных геоинформационных технологий в среде программного комплекса ArcGIS. Результаты. Установлено, что рудно-магматические системы исследуемого района соответствуют геолого-структурной позиции медно-порфировых месторождений. Изученный район объединяет группу медно-порфировых рудно-магматических систем, связанных с малыми гранитоидными интрузиями теплинского плиоцен-плейстоценового комплекса. Здесь также отмечаются рудопроявления вольфрама, мышьяка, золота, сурьмы и др., составляющие единый генетический ряд, в котором медно-порфировое оруденение занимает вполне определенную позицию, – приурочено к порфировой фазе новейшего интрузивного магматизма. Сопоставление обстановок проявления позднекайнозойского оруденения и его характеристик в пределах изученных рудоносных площадей с основными элементами типовой модели медно-порфировой системы позволяет рассматривать Сангутидонский, Теплинский и Танадонский рудные узлы как выражение надстраивающих друг друга по вертикали частей единой рудно-магматической системы медно-порфирового ти­па. Продук­тивная на медно-порфировое оруденение новейшая гранит-гранодиоритовая формация Большого Кавка­за образовалась в условиях повторноорогенного режима активизации региона и наложена на его гетерогенный субстрат. Последний в пределах изучаемого района характеризуется двухэтажным стро­ением и состоит из нижне-среднеюрского вулканогенно-осадочного комплекса чехла и доюрского основания, в котором главную роль иг­рают докембрий – нижне-среднепалеозойские метаморфические тол­щи кристаллического фундамента Большого Кавказа, прорванные пале­озойскими гранитоидами Главного хребта. Состав поздненеогеновых гранитоидов находится в зависимости от состава субстрата, как на глубинных уровнях его анатектического плавления, так и на путях подъема образованных при этом магм. В этой связи повышенная основность гранитоидов полифазного теплинского комплекса, сформированных в гипабиссальных и субвулканических условиях, обусловлена более высокой по сравнению с соседними блоками степенью мафичности субстрата исследуемого района, включающего ряд базальтоидных или близких к ним по составу толщ The article is devoted to the identification of the features of the geological structure and mineralogy of the Tanadon-Sangutidon-Kazbek district of the manifestations of copper-porphyry mineralization in the Central part of the Greater Caucasus and the assessment of the correspondence of the geological conditions of mineralization to modern models of ore-magmatic systems of the copper-porphyry type. The relevanceis determined by the need to develop a scientific and methodological basis for forecasting and searching for hidden mineralization. Aim. To identify the features of the geology and mineralogy of the Tanadon-Sangutidon-Kazbek ore region and to establish the correspondence of the mineralization conditions to modern models of ore-magmatic systems of the copper-porphyry type. Methods.Comparative geological and metallogenic analysis based on modern geoinformation technologies in the environment of the ArcGIS software package. Results. It is established that the ore-magmatic systems of the studied area correspond to the geological and structural position of copper-porphyry deposits. The studied area unites a group of copper-porphyry ore-magmatic systems associated with small granitoid intrusions of the Teplinsky Pliocene-Pleistocene complex. There are also ore occurrences of tungsten, arsenic, gold, antimony, etc., which make up a single genetic series, in which copper-porphyry mineralization occupies a well - defined position-it is timed to the porphyry phase of the latest intrusive magmatism. The comparison of the conditions of the Late Cenozoic mineralization and its characteristics within the studied ore-bearing areas with the main elements of the typical model of the copper-porphyry system allows us to consider the Sangutidon, Teplinsky and Tanadon ore nodes as an expression of the parts of a single ore-magmatic system of the copper-porphyry type superstructuring each other vertically. The newest granite-granodiorite formation of the Greater Caucasus, which is productive for copper-porphyry mineralization, was formed under the conditions of a repeated-rhogenic regime of activation of the region and superimposed on its heterogeneous substrate. The latter within the studied area is characterized by a two-story structure and consists of the Lower-Middle Jurassic volcanogenic-sedimentary complex of the cover and the Pre - Jurassic base, in which the main role is played by the Precambrian-Lower-Middle Paleozoic metamorphic strata of the crystalline basement of the Greater Caucasus, broken by Paleozoic granitoids of the Main Ridge. The composition of Late Neogene granitoids depends on the composition of the substrate, both at the deep levels of its anatectic melting, and on the ascent paths of the magmas formed during this process. In this regard, the increased basicity of granitoids of the polyphase Teplinsky complex formed under hypabyssal and subvolcanic conditions is due to a higher degree of maficity of the substrate of the studied area, which includes a number of basaltoid or similar strata in composition, compared to neighboring blocks.

Trace Element Geochemistry of Chalcopyrites and Pyrites from Golpu and Nambonga North Porphyry Cu-Au Deposits, Wafi-Golpu Mineral District, Papua New Guinea

Studying elemental geochemistry of hypogene sulphides can discriminate the hydrothermal fluids responsible for ore formation. To determine whether Golpu porphyry Cu-Au deposits are related to the Nambonga North porphyry system which is located 2.5 km apart in the Wafi-Golpu Mineral District, Papua New Guinea, we compare the trace element compositions of drill core chalcopyrites and pyrites analysed using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). The results for the Golpu chalcopyrites revealed high concentrations of Au, As, Se, Mo, Sb, Te and Bi and lower concentrations of Ag and Zn compared to those from Nambonga. Pd and Pt were below the detection limit in chalcopyrites for both deposits. The results for the Golpu pyrites indicated high concentrations of Pt, Au, Se, Mo, Sb, and Te and lower concentrations of Cu, Zn, As, Ag, Pb, Pd and Bi compared to those from Nambonga North. Au concentrations in the pyrites from both the porphyry deposits were higher compared to chalcopyrites, which mean that pyrite is the Au-bearing sulphide responsible for the higher Au content. In contrast, Cu values in pyrites from Nambonga North are higher than those from Golpu. Overall, it is envisaged that the ore fluids were exsolved at different times during the evolution of both porphyry deposits, although these porphyry centres may be related in space and time.

Zircon Petrochronology of the Kişladaǧ Porphyry Au Deposit (Turkey)

Porphyry deposits typically occur in subduction-related arcs but have more recently also been described in postsubduction, collisional to extensional back-arc settings. These different tectonic environments not only might imply different genetic processes but also seem to result in different metal endowments (e.g., Au rich versus Cu rich). It is therefore relevant, also for exploration purposes, to understand the magmatic processes involved in porphyry formation in these different tectonic environments. This study focuses on the Kişladaǧ porphyry Au (17.4 Moz) deposit in western Anatolia, which is centered on a series of porphyritic monzonite stocks of high-K calc-alkaline to shoshonitic affinity and formed in a continental rifting environment. With 17.4 Moz of Au, Kişladaǧ is of global metallogenic importance and hence a good example for studying the genetic processes associated with porphyry deposits in extensional back-arc settings. We herein combine a comprehensive set of new zircon textural observations, in situ zircon trace element and Hf isotope data, and previously published zircon geochronology to study the magmatic processes associated with porphyry deposit formation at Kişladaǧ. We show that mafic rejuvenation of a slowly crystallizing (between ~15.8 and 14.9 Ma) magma reservoir below Kişladaǧ immediately preceded porphyry deposit formation. Zircon trace elements and geochronology suggest a longer and deeper evolution for the early fertile magmas compared to the later infertile magmas. Magma evolution at Kişladaǧ was accompanied by crustal wall-rock assimilation. Whole-rock Nd and Sr radiogenic isotopes show that increasing asthenosphere-derived melt input under accelerated regional extension caused a loss in fertility of the system over time.

Zinc systematics quantify crustal thickness control on fractionating assemblages of arc magmas

Understanding the processes leading to the broad chemical variability of arc magmas is an essential, yet not fully elucidated, issue in Earth Sciences. Here, I show that Zn–MgO–SiO2 systematics of magmatic arc rocks correlate significantly with arc thickness. Because Zn–MgO–SiO2 systematics are mostly controlled by fractionation of different mineral phases, this suggests a systematic change in the proportions of fractionating mineral assemblages depending on arc thickness. Using a mass balance model with a Monte Carlo approach, I show that Zn–MgO–SiO2 systematics can be quantitatively explained by a continuous transition from plagioclase-dominated fractionating assemblages in thin arcs to amphibole-garnet-magnetite-dominated assemblages in increasingly thicker arcs. Most likely, such a systematic change results from the increase of average depth of magma differentiation that is ultimately controlled by arc thickness. Results presented have implications on the causes of different geochemical trends in arcs, the role of arcs as H2O filters, and their association with porphyry deposits.

An abrupt switch in magmatic plumbing taps porphyry copper deposit-forming magmas

Porphyry-type deposits are a vital source of green technology metals such as copper and molybdenum. They typically form in subduction-related settings from large, long-lived magmatic systems. The most widely accepted model for their formation requires that mantle-derived magmas undergo a multi-million year timescale ramp-up in volatiles and ore-forming constituents in mid- to lower-crustal reservoirs, however this does not explain why porphyry deposits are absent from the vast majority of arc magmatic systems. To address this, we have carried out geochemical and geochronological studies on the tilted, ~8 km depth equivalent, cross-section through the classic Yerington magmatic system, Nevada. Here we show that the magmas underwent a major and abrupt change in chemistry over a period of 100 kyrs which is coincident with the initiation of ore formation. This is attributed to a wholesale switch in the magmatic plumbing system whereby volatile-rich granitic melts were extracted from an estimated ~30 km depth and transported to shallow levels (~3-8 km) where exsolving fluids were focussed through highly permeable pathways to form porphyry deposits. The change in magma chemistry is documented across the entire plutonic to volcanic record. Its rapidity suggests that the increase in a magma’s ore-forming potential is not solely driven by tectonic factors, that occur over multi-million year scales, but through internal processes within the melt evolution zone, operating at more than an order of magnitude faster than previously envisaged. This short timescale narrows the temporal-geochemical footprint of magmas associated with porphyry mineralisation which will aid in targeting the next generation of ore deposits.

Metallogeny of the Lyapinsky megablock (Subpolar Urals)

Purpose of the work: elucidation of the geological structure, manifestations of magmatism, geodynamics and metallogeny of one of the largest segments of the paleocontinental sector of the Lyapin megablock in the Urals. The peculiarity of the metallogenic specialization of the latter for uranium, thorium, rare metals, gold, optical quartz caused both increased interest and contradictory ideas about its geology, composition of rock complexes, their age and genesis. Methodology of the work: generalization, analysis and synthesis of materials from long-term studies of the geology and metallogeny of the region, including experimental, methodological, thematic and geological survey work (GDP-200/2 sheets P-40-VI, P-40-XII) with the involvement of extensive literary sources. Results. For the first time, on the basis of the created formation map and the developed author’s legend of the territory, the geological structure is shown, the geological structure, geodynamic conditions of formation, metallogenic features of uneven-aged rock associations are shown. The Lyapinsky megablock, which corresponds to the Lyapinsky mineragenic zone, is a component of the West Ural megazone of the Ural Mineragenic Province, including the Mankhambovsky, Malopatoksky, Nyartinsky and Sаledsky ore nodes. In their history of development, four metallogenic epochs are distinguished: the Pre-Riphean, Riphean-Cambrian, Paleozoic and MesozoicCenozoic, specialized in noble, rare, radioactive, and non-ferrous metals, the largest objects of which include the Yasnoye, Narodnoye, Turman, Chudnoye, Sosnovoye, Telaizskoye, Torgovskoye, Turupinskoye, Kholodnoye, Kozhimskoye, and others. Conclusions. The results obtained indicate that along with a certain ore specialization of metallogenic epochs, an important factor affecting the ore content of the territory is the activated suture zones established in the course of research, in the areas where the largest ore objects, including stratiform and porphyry deposits, are localized, as well as unconventional objects of the “structural-stratigraphic disagreement” type.

Zinc Systematics Quantify Crustal Thickness Control on Fractionating Assemblages of Arc Magmas

Understanding the processes leading to the broad chemical variability of arc magmas is an essential, yet not fully elucidated, issue in Earth Sciences. Here, I show that Zn-MgO-SiO2 systematics of magmatic arc rocks correlate significantly with arc thickness. Because Zn-MgO-SiO2 systematics are mostly controlled by fractionation of different mineral phases this suggests a systematic change in the proportions of fractionating mineral assemblages depending on arc thickness. Using a mass balance model with a Monte Carlo approach, I show that Zn-MgO-SiO2 systematics can be quantitatively explained by a continuous transition from plagioclase-dominated fractionating assemblages in thin arcs to amphibole-garnet-magnetite-dominated assemblages in increasingly thicker arcs. Such a systematic change results from the increase of average depth of magma differentiation that is ultimately controlled by arc thickness. Results presented have implications on the causes of different geochemical trends in arcs, the role of arcs as H2O filters, and their association with major porphyry deposits.