Altar is a copper-gold property in San Juan province, Argentina. It is located in the Andes Mountains, approximately 10 km from the Argentina-Chile border, and approximately 180km west of the city of San Juan.
The Altar deposit was discovered in the mid-1990s by CRA. CRA completed access road construction, surface sampling (rock chip, talus fines and stream sediment), and geological mapping in the period 1995 to 1996. Geophysical data from a helicopter borne aeromagnetic and radiometric survey over the property was acquired and interpreted. In 1999, Rio Tinto completed geological mapping of the greater Altar area including Quebrada de la Mina (QDM), and did alteration studies, a ground magnetic survey, and completed seven diamond drill holes totaling 2,841 m. Peregrine Metals optioned the property in 2005, and carried out a 23.4 line-km induced polarization (IP) survey followed by eight DDH totalling 3,302 m during the 2005-2006 summer field season. In the first quarter of 2007, Peregrine carried out a second drilling campaign comprising 25 drill holes (10,408 m). Peregrine carried out a third drilling campaign in the first quarter of 2008 comprising 24 core holes and deepening of one pre-existing hole (12,741 m). Peregrine continued drilling during 2010 adding about 25,000 m of core. In October 2011, Stillwater Mining Company (SMC) completed the acquisition of all outstanding shares of Peregrine Metals Inc. Since the acquisition, Peregrine Metals has been maintained as a subsidiary as have Peregrine’s operating companies Minera Peregrine Argentina S.A. and Minera Peregrine Chile S.C.M. SMC has been actively engaged in the 2012 through 2017 Altar project activities subject to this Technical Report update as well as related Altar project developments since the time of the acquisition. In May 2017, Sibanye Gold of South Africa acquired all shares of Stillwater Mining Company, the owner of the Altar Project. However, the structure of the Altar Project subsidiaries (Peregrine Argentina S.A. and Peregrine Chile SCM) remain unchanged. In August 2017, Sibanye changed its name from Sibanye Gold to Sibanye-Stillwater. The company names and structure for Peregrine remained unchanged. Following the Sibanye-Stillwater acquisition, exploration has continued.
The Andean Cordillera extends for about 5,000 km along the western coast of South America, attaining a maximum width of about 700 km in the Central Andes of Bolivia. Tectonism in the Cordillera varies both along strike and across the range; along-strike variations reflect changing plate geometry along the Pacific margin, whereas across-strike variations generally assigned to four sub-domains reflect the generally eastward migration of Andean arc magmatism and deformation through time. In general terms, there are three units within each sub-domain, from west to east: a fore-arc zone, a magmatic arc, and a back-arc region. In the southern flat-slab sub-domain of the Central Andes (from 28°S to 33°30’S), the forearc zone is a steady rise to the crest of the Andes, which is formed by an inactive magmatic arc and thrust belt (Frontal Cordillera and Cordillera Principal). The Triassic magmatic (rift) arc has a general northwest–southeast trend. The foreland consists of an active, thin-skinned fold-thrust belt (Pre-cordillera) and zone of basement uplifts (Sierras Pampeanas, with altitudes ranging from 2,000 to 6,000 m). The Altar Project is located in the Cordillera Principal. Basement rocks in the Altar region have been assigned to the Choiyoi Group, of Permo-Triassic age; the Choiyoi Group covers about 500,000 km2 in Argentina. It comprises an upper and lower volcanic sequence, intruded by shallow-level plutons, stocks, and dyke-like bodies. The lower volcanic sequence comprises calc-alkaline andesite-dacites that represent the products of a subduction-related magmatic arc, which is overlain by an upper sequence ofperaluminous rhyolites, related to a period of post-orogenic extensional collapse. Composition of the volcanics trends from mafic to acidic through time. Both sequences are propylitically-altered and contain fracture-controlled epidote, chlorite, albite, and calcite veining. The volcanic sequence was intruded by peraluminous A-type and S-type granites that are considered coeval with the rhyolitic volcanics and likewise typically exhibit lowgrade propylitic alteration. Generally, Jurassic marine sediments that consist of red-bed sandstones and claystones infill the Triassic rift, and unconformably overlie the Choiyoi Group; however Jurassic sediments are not known in the immediate surroundings of the Altar Project. Within the Project area, rhyolitic ignimbrites and andesitic volcanics of the Pachon Formation overlie the Choiyoi basement sequence with age dates of 20 to 22 Ma (Miocene). The wider area of what comprises the Altar and Río Cenicero concessions is flanked by two significant regional north-south striking faults, referred to as the Pelambres Fault to the west, and the Río Teatinos Fault to the east of the concession area. The Pelambres fault limits the rocks of the Pachón formation against the paleogene Pelambres formation to the west. The Río Teatinos fault juxtaposes the Pachón formation against paleozoic to lower mesozoic metasedimentary and intrusive basement rocks to the east.
The Altar porphyry Cu-(Au) deposit is associated with Middle-Late Miocene intermediate composition subvolcanic porphyries that intrude Early Miocene rhyolitic ignimbrites and fine-grained andesite flows of the Pachon Formation. Elevated gold, silver and molybdenum values are associated with the copper mineralization.
The QDM deposit is located approximately 2 km to the northwest of the Altar porphyry system. QDM is hosted by the same andesite volcanic sequence that forms the country rock sequence at Altar. The QDM deposit is primarily gold and silver mineralization that is hosted in the Pachon Andesite and the Dacite Porphyry.
Early Miocene Pachon Formation – Andesites, Andesite Breccia and Rhyolites
Uncomfortably overlying the Choiyoi basement sequence is an assemblage of andesites and rhyolites of Early Miocene age, (20 to 22 Ma) which is interpreted to be part of the Pachon Formation. This formation was previously believed to be Cretaceous in age. Recent regional mapping and age dating studies have established an Early Miocene age for the Pachon Formation volcanics and time-stratigraphic equivalents in Chile, which form the country rocks to the subvolcanic porphyries responsible for the porphyry copper mineralization at
Altar, El Pachon and Los Pelambres. At Altar, the Pachon Formation comprises a volcanic-volcaniclastic sequence made up of ntercalated aphanitic basaltic andesite and porphyritic andesite-dacite lava flows, andesiticdacitic lapilli tuff and pyroclastic breccia grading upwards into an upper unit of compacted and thick rhyolitic tuffs. The most extensive outcrops of andesitic units occur on the ridges fringing the western side of the Altar mineralizing system. Outcrops of the rhyolitic unit are more widespread and rhyolites constitute the most abundant country rocks to the intrusive porphyries related to the alteration and mineralization. The contacts between andesitic and rhyolitic units of the Pachon Formation are concordant and mostly transitional. The unconformity that separates the Pachon Formation from the underlying Choiyoi basement sequence is not exposed on the Altar Project and has not been intersected in drilling.
Pachon Andesite and Pachon Andesite Breccia
The basaltic andesite is very dark in color with fine grained phenocrysts of plagioclase, ferromagnesian silicates and magnetite in an aphanitic groundmass dominantly comprised of plagioclase and ferromagnesian minerals. The porphyritic andesite-dacite flows have phenocrysts of plagioclase, ferromagnesian silicates and opaque minerals in a pilotaxitic groundmass of fine-grained plagioclase and disseminated opaque minerals. The pyroclastic units are green lapilli tuffs and clast- to matrix-supported polymictic breccias. The clasts are angular and comprised of aphanitic to porphyritic andesite and fragments of crystals set in a devitrified matrix.
The rhyolitic unit of the Pachon Formation is dominated by compact tuffs most of which can be grouped into two lithofacies: massive and eutaxitic tuffs. Massive tuff crops out abundantly at Altar Central. It has tabular fragments of plagioclase and rounded fragments of quartz in a silicified microgranular matrix. Pyroclastic features such as glass shards, fiamme and pumice fragments are obliterated by hydrothermal alteration in the vicinity of the Altar deposit. Eutaxitic tuff crops out in the ridges that surround the deposit and it comprises an ignimbrite with crystals and crystal fragments, fiamme and glass shards, and lithic fragments in a partially devitrified matrix. Crystals are generally euhedral and consist of plagioclase, quartz, biotite and opaque minerals. Lithic fragments are rounded and andesitic in composition with plagioclase phenocrysts in a pilotaxitic groundmass. On the ridges to the north of the deposit there are small outcrops of rheomorphic and parallellaminated tuffs. These are highly welded tuffs characterized by flow foliations and containing crystals and crystal fragments of plagioclase, ferromagnesian silicates and quartz, and fiamme in a partially devitrified groundmass. Samples of Pachon Formation rhyolitic tuff from Altar have returned U-Pb dates of 21.2 Ma, 21.9 Ma, and 20.0 Ma.
Middle-Late Miocene Subvolcanic Porphyry Suite
A suite of subvolcanic porphyritic stocks and dykes, and associated magmatic and hydrothermal breccias intruded the Pachon Formation volcanic complex during the Middle-Late Miocene (12 to 10 Ma). The subvolcanic stocks that produced the porphyry Cu-(Au) mineralization at Altar crop out in the central and eastern portions of the Altar cirque and the alteration and mineralization surrounding these porphyry outcrops was given the field names Altar Central and Altar East (or Central Zone and East Zone respectively) during the earliest stages of exploration drilling. Based on interpretation of recent in-fill drilling, along with petrographic analyses and geophysical IP- and CSAMT data, it is believed that a single composite stock underlies the Central and East Zones and is the source of the alteration and mineralization at Altar. The modal composition of less altered samples of the subvolcanic porphyries ranges from dacite to andesite, comprising phenocrysts of plagioclase, amphibole, biotite and quartz, along with accessory rutile, ilmenite, magnetite and apatite, in an aphanitic groundmass.
Quartz Diorite Porphyry
Porphyry stocks cropping out at Altar Central and Altar East show well developed quartz vein stockworks along with intense sericitic alteration and associated strong mineralization. These have been given the field name Early Quartz Diorite Porphyry. Though the areas where these porphyries crop out are widely separated they are petrographically indistinguishable and are believed to be derived from a single stock at depth. A sample of hydrothermal sericite from mineralized porphyry from the Central Zone gave an Ar-Ar date of 10.38 Ma, which is close to a K-Ar date of 9.8 Ma obtained from hydrothermal biotite at Los Pelambres. More recently obtained ages for the Early Quartz Diorite Porphyry from the Central and East Zones include two U-Pb dates of 9.9 Ma and 10.35 Ma from Early Quartz Diorite Porphyry from Altar Central and a U-Pb date of 10.68 Ma from the Early Quartz Diorite Porphyry stock from Altar East (Maydagan et al. in press). A Re-Os date of 10.18 Ma was obtained from molybdenite from Altar Central. A second phase of Quartz Diorite Porphyry exposed in the northern part of the Central Zone and at depth at Altar East has been given the field name Inter-mineral Quartz Diorite Porphyry. It contains less abundant quartz vein stockworks, is moderately mineralized, and is less intensely altered in comparison to the slightly older Early Quartz Diorite Porphyry. The two porphyry phases are often difficult to distinguish and clear cross-cutting relationships are scarcely seen in outcrop or drill core. Inter-mineral Quartz Diorite Porphyry was found to host medium to coarse grained, Carlsbad-twinned feldspar phenocrysts. The complex twinned phenocrysts appear to be diagnostic, as they are always present within Inter-mineral Quartz Diorite Porphyry, but less common within Early Quartz Diorite Porphyry. When this distinction is unclear the general field name Quartz Diorite Porphyry has been applied. The andesitic-dacitic subvolcanic porphyry stocks with strong hydrothermal alteration in the Central and East Zones are cut by quartz-tourmaline veins that locally form monomictic hydrothermal breccias, which are matrix-supported with clasts of subvolcanic porphyry within a quartz-tourmaline matrix. As no sharp lithological contacts and grade boundaries between the different Quartz Diorite Porphyry stocks could be determined, the different quartz diorite porphyry stocks were summarized in the 3D lithologic model under Quartz Diorite Porphyry.
Plagioclase Hornblende Porphyry
On the eastern most ridges of the Altar cirque, a distinctly different subvolcanic porphyry stock is outcropping over a large area. It is characterized by conspicuous plagioclase and hornblende phenocrysts and has been giving the field name Plagioclase Hornblende Porphyry. It hosts silica ledges related to a high-sulfidation epithermal Au-Ag system and is affected by propyllitic and advanced argillic alteration. This porphyry has a heterogeneous texture with plagioclase phenocrysts of variable size along with amphibole phenocrysts in a green submicroscopic groundmass. It can be distinguished from the other subvolcanic porphyries by the variable size of its plagioclase phenocrysts and its finer-grained groundmass that also contains a higher proportion of plagioclase. A U-Pb date of 11.75 Ma has been obtained for this porphyry.
Altar North Porphyry
During the 2011 field season, float of a new porphyry stock was discovered about 1,200 meters north of the Altar Central porphyries. The distinct subvolcanic intrusion has been given the field name Porphyry Altar North. The lithology is characterized by an equigranular crowded texture with over all smaller plagioclase and amphibole crystals than found in the Quartz Diorite Porphyry stocks. Chemistry of the Altar North Porphyry seems to be similar to the Quartz Diorite Porphyry stocks. This porphyry was first drill-tested during the 2012 drilling campaign.
The Quebrada de la Mina (“QDM”) Au-Cu prospect is located on the Altar property approximately 2 kilometers to the west of the Altar Central porphyry Cu system. QDM is underlain by the same andesitic volcanic sequence that forms the country rock sequence at Altar. The volcanics are intruded by a circular and funnel shaped Dacite Porphyry stock, approximately 700m in diameter. The Dacite Porphyry belongs to the Middle-Late Miocene Subvolcanic Porphyry Suite and is characterized by is matrix-supported porphyric texture with placioglase, biotite-books, minor amphibols and the characteristic and abundant quartz phenocrysts. Texture and chemistry of the Dacite Porphyry clearly differs from all the other intrusions described at Altar Central, Altar East and Altar North.
Colluvium and Alluvium
The Altar area was subjected to regional alpine glaciations which resulted in several moraines and significant glacial sediments that cover most low-lying areas. There is little outcrop within the altered and mineralized area due to scree and talus cover on steep slopes and glacial sediments in the valley bottoms. Glacial sediments in the Arroyo Altar area can reach up to 30 m in thickness.
All of the lithological units described in Section 7.2 have undergone varying degrees of hydrothermal alteration. The strongest alteration is found within Early Quartz Diorite Porphyry which underwent early potassic alteration (K-feldspar–secondary biotite–quartz) overprinted by intense pervasive sericitic alteration (quartz–sericite–pyrite–tourmaline). Using the vein terminology for porphyry deposits of Gustafson and Hunt (1975) at least three generations of A-veins and locally B-veins, related to potassic alteration are seen in drill core. These veins constitute typically between 10 and 30 volume% of the rock mass, but can locally reach > 50 volume%. The Inter-mineral Quartz Diorite Porphyry locally underwent potassic alteration within the core of the altered area, and is also found to have undergone weak to moderate propyllitic alteration (chlorite–specularite–quartz–hematite) peripheral to the center of the system. A-type quartz veining and K-feldspar replacement within Inter-mineral Quartz Diorite Porphyry is weak to moderate, with quartz veins generally constituting less than 20 percent of the resulting rock mass. Potassic alteration of the Quartz Diorite Porphyry phases is only preserved at depth in several of the deeper drill holes, and except in the deepest intersections has at least a weak sericitic alteration overprint. The Plagioclase Hornblende Porphyry underwent weak to moderate propyllitic alteration where outcropping and moderate to strong silic and potassic alteration at depth with a weak phyllic overprint. Phyllic alteration is not as pervasive as found in the Quartz Diorite Porphyries, and is typically related with late sulfide-rich veins. Pachon Rhyolite and Pachon Andesite also underwent potassic alteration where these units occur in proximity to Quartz Diorite Porphyry intrusions, but in all cases the resulting A-vein density was substantially less than that found in the nearby intrusions. This potassic alteration has been strongly overprinted by sericitic alteration in the shallower parts of the deposit. Drill holes of depths >500m drilled at Altar Central intercepted Pachon Rhyolite and Pachon Andesite affected by moderate to strong potassic alteration with its characteristic brown alteration color due to is abundant fine-grained hydrothermal biotite in the matrix. The sericitic alteration passes outwards into little-altered rhyolitic or chloritized andesitic volcanics, both of which were subjected to varied degrees of supergene kaolinization as a result of acid attack during pyrite oxidation. The outer limit of jarositic limonite after pyrite was mapped and defines the Altar hydrothermal system to be at least 3.5 km by 3 km in outcropping surface area. Although specular hematite is ubiquitous as a late, fracture-controlled mineral in the Altar system, it is particularly abundant in the peripheral chloritized rocks and appears to constitute a halo to the sericitic core. Epidote is apparently absent from the peripheral alteration zone, except in the northern aphanitic andesites. Intense pervasive silicic alteration is observed in drill holes at Altar East. This silicification does not appear to be related to D-vein density, and is likely associated at shallow depths with the advanced argillic alteration that affected the lithocap. Strong silicification found at Altar East at depth is associated with intense quartz veining and porphyry-style copper and gold mineralization (area of drill hole ALD 148). Pervasive sericitic alteration as found at Altar Central is not present in this part of the deposit.
Stockwork quartz veining was initially identified in surface mapping. It comprises grey to pinkish-grey, translucent A-type quartz veins as well as a lesser number of more laterally extensive B-type quartz veinlets characterized by central sutures. The A-type veinlets attain 3 cm in width. The stockwork zones are cut by generally minor D-type veinlets with prominent sericitic haloes; the most extensive observed examples from surface exposures in the western stockwork zone strike north–northeasterly, parallel to the zone itself.
The 3 km long arcuate ridge along the eastern side of the Altar cirque is characterized by the basal part of an advanced argillic lithocap. The lithocap remnant is defined by numerous structurally-controlled silica ledges separated by chloritized Plagioclase Hornblende Porphyry. In 2008 approximately 50 principal ledges were mapped to define a broadly radial pattern centered on the eastern stockwork zone. Mapping by Peregrine in 2009 defined over 200 ledges. Ledges are confined to the ridge top, at elevations above 3,600 m and do not continue far down the talus-covered slopes. Most ledges are steep and contain main zones, ranging in width from 10 cm to 2 m, of quartz–alunite alteration flanked outwards by quartz–kaolinite. Locally, pyrophyllite is observed as a transitional zone. A few ledges contain pods of vuggy residual quartz along their center(s) lines in which enargite and, less commonly, barite and native sulphur occur. Stringers of massive enargite are also present in places in quartz-rich quartz–alunite ledges lacking vuggy quartz. The hypogene quartz–kaolinite haloes to the ledges are transitional outwards to supergene kaolinization developed at the expense of chlorite–smectite alteration. The most extensive ledge, 500 m long, terminates in a small hydrothermal breccia pipe displaying intense quartz–alunite alteration.
Outcrop mapping in the northern part of the Altar cirque has identified an inferred northnortheast-striking fault projected to cut through the center(s) of the mineralized system between Altar Central and Altar East. Grey fault gouge exposed in a road cut at Gauss Kruger coordinates 2,359,750E/6,516,830N provides further evidence for the continuity and importance of this fault zone. This may also be reflected by zones of intense fracturing intersected in drill holes ALD 01, ALD-03, ALD 08 and ALD 09. The CSAMT geophysical survey done in 2011 possibly indicates a structure between Altar Central and Altar East. Geostatistical studies done for the resource calculation support the assumption of the northnortheast-striking fault. The silica ledges which define the basal part of the advanced argillic lithocap are much more numerous on the ridge crests on the east side of the inferred fault than on the west side, where only a few silica ledges occur at the highest elevations. This suggests west side up displacement across the fault system. Deeper levels of the stratigraphic succession are exposed on the west side of the fault, again implying west-side up displacement.
Surface geological and alteration mapping, IP geophysical surveys and drilling have identified porphyry-and high-sulfidation-related alteration and sulfide mineralization at Altar, extending over an area of 2.9 km by 1.7 km within a 3.5 km by 3 km zone of hydrothermal alteration.
Mineralization at the Altar deposits is closely associated with the different porphyry stocks and related hyrothermal breccias, but is also found in Pachon Rhyolite, Pachon Andesite and Pachon Volcanic Breccia. The well-developed copper mineralization shows a strong relationship to the distribution and intensity of sericitic and potassic alteration.
Peregrine geologists have interpreted the mineralization paragenesis as follows.
▪ Stage 1: Potassic alteration, accompanied by deposition of pyrite-chalcopyrite-bornite and pyrite-molybdenite mineralization.
▪ Stage 2: Sericitic alteration overprint, accompanied by reconstitution of the Stage 1 mineralization as assemblages of pyrite, chalcocite, and bornite.
▪ Stage 3: Deposition of pyrite–enargite vein systems.
▪ Stage 4: Supergene digenite and covellite overprinting hypogene pyrite, chalcopyrite, and bornite and chalcocite mineralization.
Acidic high sulfidation conditions prevalent in an advanced argillic lithocap were superimposed on an underlying potassic alteration zone as a result of telescoping. Hypogene sulphides generally exhibit a consistent vertical zonation pattern: pyrite–enargite at the higher levels; pyrite–chalcocite–bornite assemblages at intermediate levels; and pyrite–chalcopyrite–bornite and pyrite–molybdenite assemblages at deeper levels. Recent petrographic work has also identified tennantite-tetrahedrite from intermediate level samples. Supergene covellite and digenite occur as an overprint on hypogene sulphides within sericitic alteration, descending from the base of oxidation beneath the leached capping at high levels to intermediate depths.
The copper mineralization associated with the potassic alteration, mainly porphyry style chalcopyrite–bornite mineralization, was reconstituted as hypogene assemblages of pyrite, chalcocite and bornite within the sericitic alteration zone. Magnetite originally present in the potassic alteration zone was pyritized during the high sulfidation overprint. Sulfide minerals found within sericitic alteration include hypogene pyrite, chalcopyrite, chalcocite, enargite, bornite, and molybdenite along with supergene covellite and digenite. Latest stage pyrite
enargite veins related to a high sulfidation epithermal system cut through the Stage 1 and 2 mineralization, but contribute a minor proportion of the copper mineralization.
Pyrite is ubiquitous with contents ranging from 2 to 15 percent but generally falling between 3 percent and 6 percent. It occurs as disseminations in wall rock, as quartz–pyrite veins, in late pyrite–enargite veins and occasionally as massive pyrite veins up to 2 cm thick.
The main style of hydrothermal alteration observed at the arcuate ridge at Altar East on the Rio Cenicero property corresponds to a potential high sulfidation epithermal gold system that is located in the northern half of the RCA XII concession. Advanced argillic alteration is associated with the epithermal mineralization and is accompanied by widespread silicification in the form of silica ledges, which are steeply dipping structures filled with epithermal quartz.
Peregrine mapped a large number of silica ledges within the zone of advanced argillic alteration in the RCA XII concession. The silica ledges are characterized by vuggy silica, multi-stage episodic hydrothermal breccias (crackle breccias and rotational breccias, and breccias with well-rounded clasts that indicate forceful expulsion of high-pressure fluids), colloform and crustiform banded quartz, deposition of native sulphur, alunite, barite, enargite and tennantite, limonite and boxworks after sulfides. These are indicators of the high level acid sulfate environment that overlies high sulfidation epithermal gold deposits.
In 2011 Peregrine discovered with drill hole ALD 148 at Altar East a new zone of primary chalcopyrite-bornite mineralization associated with a strong quartz vein stockwork. Millimeter thick sheeted dark quartz veinlets, the radial orientation of the previously mapped and sampled silica ledges and a Cu-Mo-Au surface geochemistry anomaly were the only surface evidences for potential Cu-Au mineralization at depth. The 2012 and 2013 follow-up exploration drilling confirmed an extensive zone of quartz vein stockwork and associated chalcopyrite and bornite mineralization at depth. Best mineralized intercepts correspond to a strong quartz vein stockwork with distinctively fragmented quartz veins in strongly silicified Plagioclase Hornblende Porphyry. Higher copper and gold grades correlate with the bornite/chalcopyrite ratio – the more bornite observed, the higher are copper and gold grades.
The Quebrada del la Mina (QDM) deposit is primarily a gold deposit with minor associated copper. The Pachon Andesite volcanics were intruded by a circular dacite porphyry stock approximately 700 m in diameter and host a large alteration footprint centered on the porphyry stock. Surface rock exposures at QDM are characterized by pervasive quartzsericite-tourmaline alteration with disseminations and veinlet stockworks of jarosite after pyrite and less-abundant fine quartz veinlets. The area affected by the alteration is coincident with the center of an induced polarization (“IP”) geophysical anomaly that measures 300 meters by 900 meters, as defined by the 20 millivolt per volt chargeability contour on the 3,500 meter elevation level plan.
Visible oxide copper mineralization occurs in the alteration zone at QDM and includes malachite, chalcanthite, neotosite and azurite impregnating fractures. Sphalerite mineralization of up to a few percent in volume was observed in several surface exposures in the northern and eastern part of the alteration footprint. Well-defined hydrothermal breccias occur at the eastern contact between the dacite intrusion and the andesitic host rocks. Three campaigns of geochemical rock chip sampling have consistently returned gold grades ≥0.5 g/t along with low copper grades reflecting the fact that the rocks at surface are leached of more mobile copper while leaving behind the immobile gold. The 2011 and 2012 exploration drilling at QDM confirmed significant Au mineralization in the leached capping and the underlying sulfide zone, where Au mineralization is associated with abundant pyrite dissemination.
At Altar, a leached cap zone has been intersected by drilling at depths ranging from zero to 258 m. Below the leached capping is a zone of primarily sulfide mineralization that is variably affected by weathering, mainly in the form of oxidation developed along narrow joints and fractures. This transitional zone, usually referred to as mixed zone, ranges from 4 to a maximum of 86 m and has an average thickness of about 11 m. In most drill holes at Altar Central the transition between the leached cap zone to the sulfide zone is a well-defined boundary. Leached capping at Altar East in the area of ALD 148 is very shallow and typically does not exceed 30 meters depth.
Sulfide mineralization at Altar has been logged at depths ranging from 9 to 1166 m. Drilled thicknesses range from about 110 m in drill hole ALD 09, to 1140 m in ALD 179. All but 4 holes completed to date that have reached target depth have ended in sulphide mineralization, and the mineralization remains open at depth, including the deepest hole to date ALD 179.
Mineralization thickness at QDM is approximately 220 m for mineralization with grade above 0.20 gm/t.
The Altar Project contains copper ± gold ± molybdenum sulfide mineralization that was deposited in an environment that transitions from the basal roots of a high sulfidation epithermal lithocap to a sub-volcanic porphyry copper environment at depth. The Altar Project is described as telescoped because of the close spatial distance between the porphyry and high sulfidation alteration systems. High sulfidation epithermal characteristics of the Altar porphyry system have been preserved locally at higher topographic elevations and are most notable along the arcuate ridge at the eastern margins of Altar East. The age of the porphyry copper mineralization is now constrained by recently obtained geochronological results to approximately 12 to10 Ma, however there are as yet no reliable published dates for the epithermal mineralization that overlies it and the direct temporal genetic link between the two types of mineralization remains conjectural.
High-Sulfidation Epithermal Deposits
These deposits typically form in subaerial volcanic complexes or composite island arc volcanoes above degassing magma chambers. The deposits are also genetically related to high level intrusions. Multiple stages of mineralization are common, presumably related to periodic tectonism with associated intrusive activity and magmatic hydrothermal fluid generation. High sulfidation deposits can also be developed in second order structures adjacent to crustal-scale fault zones, both normal and strike slip, as well as local structures associated with sub-volcanic intrusions. The deposits tend to overlie and flank porphyry copper-gold deposits and underlie acid leached siliceous, clay and alunite-bearing lithocaps.
Host rocks are typically volcanic pyroclastic and lavas, most commonly subaerial andesite to dacite and rhyodacite, and their sub-volcanic intrusive equivalents. The deposits range in age from Tertiary to Quaternary; less commonly, Mesozoic and rarely Palaeozoic volcanic belts may be hosts. The rare preservation of older deposits reflects rapid rates of erosion before burial of subaerial volcanoes in tectonically active arcs. Mineralization is developed in multiple, cross cutting veins and massive sulfide replacement pods and lenses, stockworks and breccias. Deposits may have irregular shapes, as deposit geometry is determined by host rock permeability and the orientation of deposition controlling structures. Principal minerals comprise pyrite, enargite/luzonite, chalcocite, covellite, bornite, gold, and electrum; lesser minerals can include chalcopyrite, sphalerite, tetrahedrite/tennantite, galena, marcasite, arsenopyrite, silver sulphosalts, and tellurides including goldfieldite. Two types of ore are commonly present: massive enargite-pyrite and/or quartz-alunite-gold.
Typically, alteration consists of quartz, kaolinite/dickite, alunite, barite, hematite; sericite/illite, amorphous clays and silica, pyrophyllite, andalusite, diaspore, corundum, tourmaline, dumortierite, topaz, zunyite, jarosite, Al-P sulfates (such as hinsdalite, woodhouseite, crandalite) and native sulfur. Advanced argillic alteration is characteristic, and can be a really extensive and visually prominent. Quartz occurs as fine-grained replacements and, more characteristically, as vuggy residual silica in acid-leached rocks.
Porphyry Copper Deposits
Porphyry copper deposits tend to form in orogenic belts at convergent plate boundaries, and are commonly linked to subduction related magmatism and subvolcanic intrusions. They may also form in association with emplacement of high level stocks during extensional tectonism related to strike slip faulting and back-arc spreading following continent margin accretion. Virtually any type of country rock can be mineralized, but commonly the high level stocks and related dykes intrude their coeval and cogenetic volcanic piles. Porphyry
deposits in the Andes are generally Tertiary in age; globally, deposits can range in age from Archaean to Quaternary.
Intrusions range from coarse grained phaneritic to porphyritic stocks, batholiths and dike swarms, but are rarely pegmatitic. Compositions range from calc-alkaline quartz diorite to granodiorite and quartz monzonite. Commonly, there are multiple emplacements of successive intrusive phases and a wide variety of breccias. Deposits generally comprise large zones of hydrothermally altered rock that contain quartz veins and stockworks, sulfidebearing veinlets, fractures and lesser disseminations in areas up to 10 km2 in size. Deposits can be wholly or in part coincident with hydrothermal or intrusion breccias and dike swarms. Deposit boundaries are determined by economic factors that outline ore zones within larger areas of low grade, concentrically zoned mineralization.
Pyrite is the predominant sulfide mineral; in some deposits the iron oxide minerals magnetite, and rarely hematite, are abundant. Economically important minerals are chalcopyrite; molybdenite, lesser bornite and rare (primary) chalcocite. Subordinate minerals are tetrahedrite/tennantite, enargite and minor gold, electrum and arsenopyrite. In many deposits, late veins commonly contain galena and sphalerite in a gangue of quartz, calcite and barite.
Early formed alteration can be overprinted by younger assemblages. Central and early formed potassic zones (K-feldspar and biotite) commonly coincide with ore. This alteration can be flanked in volcanic host rocks by biotite rich rocks that grade outward into propylitic rocks. The biotite is a fine-grained secondary mineral that is commonly referred to as an early-developed biotite or a biotite hornfels. These older alteration assemblages in
cupriferous zones can be partially to completely over printed by later biotite and K-feldspar and then phyllic (quartz–sericite–pyrite) alteration, less commonly argillic, and rarely, in the uppermost parts of some ore deposits, advanced argillic alteration (kaolinite–pyrophyllite).
Alternatively, a porphyry system may exhibit hypogene enrichment. The process of hypogene enrichment may relate to the introduction of late hydrothermal copper enriched fluids along structurally prepared pathways, or the leaching and redeposition of hypogene copper, or a combination of the two. The enriched copper mineralogy comprises, for example, covellite and chalcocite. Such enrichment processes result in elevated hypogene grades.
Supergene enrichment of porphyry deposits may occur during tectonic uplift and coevel erosion processes and episodes of favorable semi-arid climate, when meteoric water percolates through the topmost parts of the deposit, thereby oxidizing primary sulfides. This process leads to the formation of sulfuric acid. Acidic meteoric waters leach metals and carry them downward to react with primary sulfides at the redox boundary, e.g. the paleo water table. This reaction produces secondary sulfide mineralization such as chalcocite, covellite and digenite. For supergene enrichment to take place a balance between uplift, climate, rock composition and structure is required.
The Altar deposit exhibits moderate supergene enrichment as observed in logs and measured by the sequential copper assays in the data base.
Altar deposit - lithology plan. Source: Peregrine Metals Ltd.
Geological Section 6,516,700 mN, Looking North Source: Peregrine Metals Ltd.
Source: TECHNICAL REPORT ESTIMATED MINERAL RESOURCES 2018