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Schematic illustration of alteration zoning and overprinting relationships in a porphyry system (modified after Holliday and Cooke 2007; Cooke et al. 2014). Lithocaps can overlie and partially overprint porphyry-style mineralisation associated with shallowcrustal hydrous intrusive complexes. They may host high sulfidation-state mineralisation and can cover intermediate sulfidation state epithermal veins. The lithocaps will overprint and be surrounded by propylitic alteration assemblages that vary from high to low temperature alteration subfacies (i.e., actinolite, epidote and chlorite subfacies) as a function of proximity to the intrusive source. The roots of the lithocap lie within the pyrite halo of the porphyry system. The degree of superposition of the lithocap into the porphyry system is contingent on uplift and erosion rates at the time of mineralization, and will vary from province to province, and from district to district. Abbreviations: ab-albite; act-actinolite; anh-anhydrite; Au-gold; bi-biotite; bn-bornite; cb-carbonate; chl-chlorite; cp-chalcopyrite; epi-epidote; gt-garnet; hm-hematite; Kf-K-feldspar; mt-magnetite; py-pyrite; qz-quartz. 

Schematic illustration of alteration zoning and overprinting relationships in a porphyry system (modified after Holliday and Cooke 2007; Cooke et al. 2014). Lithocaps can overlie and partially overprint porphyry-style mineralisation associated with shallowcrustal hydrous intrusive complexes. They may host high sulfidation-state mineralisation and can cover intermediate sulfidation state epithermal veins. The lithocaps will overprint and be surrounded by propylitic alteration assemblages that vary from high to low temperature alteration subfacies (i.e., actinolite, epidote and chlorite subfacies) as a function of proximity to the intrusive source. The roots of the lithocap lie within the pyrite halo of the porphyry system. The degree of superposition of the lithocap into the porphyry system is contingent on uplift and erosion rates at the time of mineralization, and will vary from province to province, and from district to district. Abbreviations: ab-albite; act-actinolite; anh-anhydrite; Au-gold; bi-biotite; bn-bornite; cb-carbonate; chl-chlorite; cp-chalcopyrite; epi-epidote; gt-garnet; hm-hematite; Kf-K-feldspar; mt-magnetite; py-pyrite; qz-quartz. 

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Lithocaps are subsurface, broadly stratabound alteration domains that are laterally and vertically extensive. They form when acidic magmatic-hydrothermal fluids react with wallrocks during ascent towards the paleosurface. Although lithocaps typically have steeplydipping structural roots, there is a significant component of lateral fluid flow involv...

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... i. Hypogene AA alteration environment This environment is formed by hypogene acidsulfate-chloride condensates separated from a mixture of vapor and hypersaline liquid at depth from a shallow intrusion source, generating a highly acidic fluid (pH < 1.5) that forms the lithocap in the upper portions of porphyry copper systems (Sillitoe 1995(Sillitoe , 2010Hedenquist and Arribas 2021). The study area surface shows sulfate-rich mineral assemblages consisting mainly of quartz-alunite-kaolinite that typically develop in the upper parts of these systems (Sillitoe 2010; Hedenquist and Taran 2013; Cooke et al. 2017). There is a core of silicified rock with restricted residual quartz zones at the upper areas of the Coya hill in which fractures, feeders, and veins are flanked by host rocks containing quartz-alunite ± kaolinite or quartz-kaolinite (or dickite) mineral assemblages, which grade laterally and downward, to clay minerals, mainly kaolinite-smectite ± illite/smectite (Fig. 3a, b). ...
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... The lithocap, first defined by Sillitoe (1995), is a volumetrically significant domain of pyrite-rich rocks with extensive hypogene silicic, advanced argillic, and argillic alterations that formed between a paleosurface and a shallow-crustal intrusion. It is helpful for the finding of underlain porphyry mineralization by a lithocap due to its prominence on the surface (Sillitoe, 1995(Sillitoe, , 2000Hedenquist et al., 1998;Cook et al., 2017). However, the presence of a large lithocap (up to tens of square kilometers) maybe hinder the work of finely alteration zoning to further pinpoint the location of the underlying intrusive center. ...
... Intense volcanic activities are accompanied by mineralization, which is characterized by plentiful non-metallic alteration and mineralization, such as alunite, pyrophyllite, dickite, and illite. The non-metallic mineralization is supposed to have an affinity with Au-Cu-Mo polymetallic deposits and is an indicator of the blind metallic ore most of the time (Sillitoe, 2010;Chang et al., 2011;Hedenquist and Taran, 2013;Cook et al., 2017;Chen et al., 2019). The Guihu pyrophyllite deposit and the Fanshan alunite deposit are the representative non-metallic deposits in the area. ...
... According to the updated model (Sillitoe, 1995(Sillitoe, , 2000(Sillitoe, , 2010Hedenquist and Taran, 2013), magmatic fluid exsolved from water-rich intrusions in the shallow crust, forming supercritical fluid. The supercritical fluid underwent phase separation due to the decrease of pressure as it goes up, forming a huge volume of vapor and a relatively small volume of brine (Bodnar et al., 1985;Hedenquist et al., 1998;Cook et al., 2017). Some gas may escape from the volcanic vent, but most of the vapor carrying a large amount of acid-rich volatile (HCl and SO 2 ) condensed and reacted with the surrounding rock, producing advanced argillic alteration. ...
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... At a first order of approximation, these RTE anomalies may be explained by the Imbanguila Dacite which is more magnetic (low RTE anomalies) vis-à-vis the less magnetic, hydrothermally-altered surrounding rocks (high RTE anomalies). In addition, the presence of alunite in Mohong Hill is consistent with a lithocap (Chang et al., 2011) which could possibly overlie an associated porphyry copper deposit at depth (e.g., Sillitoe, 1983;Sillitoe, 2010;Cooke et al., 2017). ...
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... A lithocap is a type of alteration system that has undergone advanced argillic and argillic alteration and is mainly composed of acidsulfate alteration minerals characterized by alunite-kaolinite-dickite-quartz ± pyrite (Rye et al., 1992;Sillitoe, 1995). Lithocaps generally occur in island arc settings above convergent plate boundaries (Sillitoe et al., 1998;Cooke and Simmons, 2000;Sillitoe, 2010;Xu et al., 2010;Richards, 2011) and are hosted in volcanic strata along well-permeated or fractured structures (Sillitoe, 1995;Cooke et al., 2017b). A lithocap is generally related to porphyry intrusions (Steven and Ratte, 1960;Cooke et al., 2014Cooke et al., , 2017a and have long been for exploration. ...
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... The recognition of fertile belts of igneous intrusions and prospective areas of hydrothermal alteration can now be assisted through the use of porphyry indicator minerals (PIMs) such as zircon, plagioclase, apatite, magnetite and tourmaline (Dupuis & Beaudoin 2011;Dilles et al. 2015;Shen et al. 2015;Bouzari et al. 2016;Williamson et al. 2016)such minerals can help to identify the geochemical 'fingerprint' of a porphyry deposit and discriminate it from other deposit styles and background rocks. At the district scale, far-field detection of concealed mineralized centres in porphyry districts has been enabled through the application of porphyry vectoring and fertility tools (PVFTs), which involves detection of low-level geochemical anomalies preserved in hydrothermal alteration minerals such as epidote, chlorite or alunite (Chang et al. 2011;Cooke et al. 2014aCooke et al. , 2015Cooke et al. , 2017Wilkinson et al. 2015Wilkinson et al. , 2017Baker et al. 2017;Xiao et al. 2018). This new generation of geochemical exploration tools have been created due to advances in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and hyperspectral analytical techniques. ...
... Lithocaps may form between the mineralizing intrusive complex and the paleosurface (Fig. 2). Lithocaps are large, stratabound domains of silicic, advanced argillic and argillic alteration assemblages that can exceed dimensions of 10 × 10 km laterally and may be more than 1 km thick (Sillitoe 1995;Chang et al. 2011;Cooke et al. 2017). Lithocaps typically have structural roots, with advanced argillic assemblages transitioning downwards from quartz alunitepyrite to quartzdickitepyrophyllitepyrite and then into phyllic-altered roots (i.e. ...
... quartzmuscovitepyrite; Sillitoe 1999). Lithocaps provide significant challenges for explorers because they have very broad, difficult to detect lateral alteration zonation patterns defined by clay minerals (Chang et al. 2011;Cooke et al. 2017). ...
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... In many districts, pre-ore alteration is associated with the development of laterally continuous lithocaps of often lithologically controlled blankets or ledges of advanced argillic alteration, representing the upper expressions of magmatichydrothermal systems ( Fig. 2; Sillitoe, 1995Sillitoe, , 2010Hedenquist et al., 2000;Cooke et al., 2017;John et al., 2018). Extensive lithocaps, with their surrounding argillic alteration, can obscure areas of underlying blind mineralization (Teal and Benavides, 2010;Cooke et al., 2017;Fig. ...
... In many districts, pre-ore alteration is associated with the development of laterally continuous lithocaps of often lithologically controlled blankets or ledges of advanced argillic alteration, representing the upper expressions of magmatichydrothermal systems ( Fig. 2; Sillitoe, 1995Sillitoe, , 2010Hedenquist et al., 2000;Cooke et al., 2017;John et al., 2018). Extensive lithocaps, with their surrounding argillic alteration, can obscure areas of underlying blind mineralization (Teal and Benavides, 2010;Cooke et al., 2017;Fig. 29A). ...
... Large, disseminated high-sulfidation epithermal deposits often occur in lithocap environments, as exemplified by Pascua, Veladero, Tambo (Chile), Yanacocha, Lagunas Norte/ Alto Chicama (Peru), Mulatos-La India (Mexico), Paradise Peak (Nevada), and several deposits on the Biga Peninsula of Turkey (Sillitoe, 1999;Bissig et al., 2015;Sanchez et al., 2016). Paleoupflow zones within the lithocap can be inferred from the distribution of zones of strong silicification and residual quartz alteration, which often are preserved as topographic highs due to preferential erosion of surrounding argillic steam-heated alteration (Fig. 29D, E; Vikre, 1989;Cooke et al., 2017). Fault-controlled paleoupflow zones may be indicated by thickening of silicified zones within the lithocap (Fig. 29B), forming resistant, linear anomalies and ore zones ( Fig. 29C; Harlan et al., 2005;Teal and Benavides, 2010). ...
... The recognition of fertile belts of igneous intrusions and prospective areas of hydrothermal alteration can now be assisted through the use of porphyry indicator minerals (PIMS) such as zircon, plagioclase, apatite, magnetite and tourmaline (Dupuis and Beaudoin, 2011;Dilles et al., 2015;Shen et al., 2015;Williamson et al., 2016;Bouzari et al., 2016). At the district scale, far-field detection of concealed mineralized centres in porphyry districts can now be enabled through the application of porphyry vectoring and fertility tools (PVFTS), which involves detection of low-level geochemical anomalies preserved in hydrothermal alteration minerals such as epidote, chlorite or alunite (Chang et al., 2011;Cooke et al., 2014aCooke et al., , 2015Cooke et al., , 2017Wilkinson et al., , 2017Baker et al., 2017;Xiao et al., 2017). This new generation of geochemical exploration tools has arisen thanks to advances in laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analytical techniques. ...
... These subzones essentially map the actinolite and epidote isograds (Figure 3), and represent decreasing fluid temperatures and oxygen fugacity away from the intrusive complex (Cooke et al., 2014a). Magnetite and Figure 3: Schematic illustration of alteration zoning and overprinting relationships in a porphyry system (modified after Holliday and Cooke 2007;Cooke et al. 2014bCooke et al. , 2017. The multiphase intrusive complex at the centre of porphyry deposits typically has potassic alteration developed within and around it. ...
... Lithocaps may form between the mineralizing intrusive complex and the paleosurface (Figure 3). Lithocaps are large, stratabound domains of silicic, advanced argillic and argillic alteration assemblages that can exceed dimensions of 10 x 10 km laterally and may be more than 1 km thick (Sillitoe, 1995;Chang et al., 2011;Cooke et al., 2017). Lithocaps typically have structural roots, with advanced argillic assemblages transitioning downwards from quartzalunitepyrite to quartzdickitepyrophyllitepyrite and then into phyllic-altered roots (i.e., quartzmuscovitepyrite; Sillitoe, 1999). ...
Chapter
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Article
The Ulandryk and related prospects in the Altaid orogenic belt (near the Russian-Mongolian border) comprise intense iron oxide (hematite), Cu, REE, and locally U mineralization and are estimated to contain in excess of 240 Mt iron oxide ores and 3.7 Mt copper. These prospects bear many signatures of the “classic” IOCG (-REE, U) deposits typical of Precambrian terranes but, in contrast, are situated in a Phanerozoic (Paleozoic) setting. They are related to the Early Devonian subvolcanic potassic granite stocks with transitional shoshonitic to A-type granite signatures suggesting a post-orogenic (post-collisional) setting, with some anorogenic (intracontinental to within-plate) affinity. The stocks have been intruded into a coeval local volcanic structure (a volcanic dome complicated by the central caldera) composed of Devonian trachyandesite, trachydacite, quartz latite, rhyolite, rhyolite-dacite, and dominant trachyrhyolite lavas, tuffs and subovolcanic porphyry intrusions. The granitic stocks are accompanied by magmatic and multi-staged hydrothermal breccias, zones of sodic (albite-quartz), potassic (quartz-K-feldspar), propylitic (quartz-albite-chlorite-amphibole) and dominant phyllic to carbonate-phyllic (quartz-sericite to quartz-sericite-carbonate) to possibly argillic (quartz-kaolinite) alteration, with intense development of hematite. Fluorite is also ubiquitous and locally abundant. The mineralization occurs in several wide (typically 60-100 m, up to 200 m) and extended (1.4-6 km) linear to arc-like paralleling steeply dipping zones of breccias surrounding the granite stocks, with the host rock and quartz fragments cemented by fine-grained quartz-hematite and coarser hematite (specularite) material. Copper-gold, REE, and locally U mineralization overprints hematite-rich zones. Wider quartz-sulfide stockworks with Cu-Au mineralization zones containing minor to trace hematite are also present. Quartz is generally abundant forming quartz-hematite veins, stockworks, and breccias (locally with crustiform texture), and zones of quartzite-like pervasive silicification (typically with sericite and clay minerals). Fluid inclusions in quartz contain daughter halite crystals and homogenize by halite dissolution after vapor bubble disappearance indicating a homogenous, high-salinity (35-45 wt.%), Na-Ca-K-chloride, aqueous mineralizing fluid. The relatively low homogenization temperatures (∼200-260°C) and generally subvolcanic-level pressure (∼0.2-0.5 kbar) conditions suggest a shallow level of mineralization possibly corresponding to an upper (to the uppermost) part of a vertically extended magmatic-hydrothermal system.