Revelo Resources announced that a new porphyry copper-gold target has been identified at Melissa in the northeastern quadrant of its wholly-owned Montezuma Project.
The Company has identified a 600m x 400m area of interest, within a much larger hydrothermally altered zone, coinciding with a number of historic, artisanal workings characterised by narrow structures filled with massive copper-rich chalcocite. The target area, which has never been drill tested, has characteristics of the transition from a sub-epithermal, carbonate-base-metal system to a porphyry copper-gold system at depth. The structurally-controlled chalcocite mineralisation maybe the result of supergene enrichment of primary chalcopyrite related to a possible porphyry copper-gold source at depth.
Tim Beale, President and CEO of Revelo, commented: "We are pleased that our in-house exploration and review work at Montezuma, as previously announced, has resulted in the definition of a new copper target at Melissa. Detailed field work and a comprehensive review of historic information, including re-logging of historic drill holes, has been key to understanding the new target. Montezuma is a very large property with several priority targets of interest, situated at the heart of one of the world's most important copper-mining districts – midway between the giant Chuquicamata and Centinela copper mines in northern Chile.
"Our work program, led by an experienced, Chilean consultant geologist, will now shift to the highly prospective central part of the Montezuma property, where we will review and evaluate the target C-A-B area, which covers approximately 10 km of the north-south oriented West Fissure Fault Zone. The ongoing work includes detailed geological mapping, spectral studies of hydrothermal alteration mineralogy, re-logging of drill holes, and reinterpretation of geochemical and geophysical surveys."
MELISSA GEOLOGIC OVERVIEW
Previous workers at Melissa had revealed widespread, multi-element geochemical anomalies, including copper, molybdenum and gold values, associated with a large, approximately 3-4 km diameter area of hydrothermal alteration and small, historic mineral workings – mostly for copper, but some for gold. Trenching and pitting, mostly around artisanal workings, was followed by a short drilling programme with wide-spaced holes testing several targets at the end of 2013 and early 2014. Further work in 2015 to 2016 was directed towards further geochemical sampling programs both in the outcropping Melissa area and in the post-mineral covered area to the north, followed by a limited, 2-hole drilling program in the post-mineral covered area, but with neither hole penetrating the gravel cover and testing the bedrock.
Geology at Melissa consists of a Paleozoic sequence of porphyritic andesites and quartz sandstones intruded by a granite and granodiorite plutonic complex, also of Paleozoic age. Widespread intermediate-argillic alteration, frequently associated with carbonate or quartz-carbonate veins and veinlets, affects these rocks over an area of at least 4 km east-west by 3 km north-south.
The area of outcrop is terminated to the north by a significant fault zone trending east-northeast that controls a Miocene – Pliocene gravel and caliche-filled basin, which extends all the way to the mining town of Calama some 10 km to the north, and which has been explored by multiple companies over a period of at least 25 years for covered porphyry copper targets.
In the central-eastern part of Melissa, the intermediate-argillic alteration, characterised by the alteration of feldspar crystals to green illite-smectite, the destruction of mafic minerals, and accompanied by several phases of quartz-carbonate veining, is in transition to phyllic alteration, characterised by the presence of sericite and/or phengitic sericite, and accompanied by lesser quartz-carbonate veinlets and the occurrence of "D" type veins and veinlets with hematitised sutures and typical sericitic alteration halos. The area transitioning to phyllic alteration is elongated northwest-southeast, sub-parallel to local faulting, and covers an area of approximately 2,000m by 500m. Some areas display patches of coarse-grained, pervasive sericite. Earthy, red hematite is commonly associated with the phyllic alteration as disseminations and in veinlets, and some specular hematite also occurs. Late iron-rich carbonates and manganese oxides are widespread as impregnations, in veinlets and as fracture fillings.
On the western edge of the area transitioning to phyllic alteration, a sub-area approximately 600m east-west by 400m north-south, is characterised by the more frequent presence of sericite, lesser carbonate, and strong earthy hematite staining that forms a "cap". Several historic, artisanal copper workings are concentrated around this zone. These workings, together with some historic exploration trenches, reveal the presence of structurally-controlled, massive, supergene chalcocite (copper-rich sulphide) veins and veinlets that are being oxidised in surface exposures to brochantite and malachite (green oxide copper minerals) in the top few metres. The workings follow generally sub-vertical mineralised structures that are oriented north-south. The copper workings are thought to be focused around the margins of the area displaying phyllic alteration, as the presence of abundant carbonate in the surrounding intermediate argillic altered rocks may have acted as a buffer for the precipitation of metals from both hypogene and supergene mineralising solutions in the veins.
In-house mineral spectrometry work on hand samples has revealed the presence of the mineral kutnohorite (calcium-manganese carbonate) associated with the copper-mineralised zones. This mineral has been described in academic studies from the southwest Pacific as indicating the geological transition from the higher-level epithermal environment to the deeper-level porphyry environment in porphyry-related copper-gold systems. The mineral spectrometry has also validated the main alteration and mineralization minerals observed in the field.
Minor, artisanal mineral workings centred on quartz-carbonate veins with copper oxides and possibly gold mineralisation, some of them distributed as far as 2 km to the southwest of the intermediate argillic / phyllic transition described above, reveal the Melissa target to be part of a larger mineralised area within the overall alteration zone. These peripheral workings typically show epithermal geochemical signatures including the presence of highly anomalous arsenic-antimony-bismuth pathfinders, which suggest a zoning pattern around the target area.
Historic drilling results outside of the main target area also support the interpreted zonation patterns, and are indicative of a fertile hydrothermal system. A historic target with anomalous copper, gold and arsenic geochemistry in rock samples located 1 km west of the target area, was the subject of three historic diamond drill holes with several anomalous intercepts, including hole MM11 that cut multiple, narrow anomalous zones with increasing copper with depth, such as 4.5m @ 1.76g/t Au + 7,571ppm As + 194ppm Cu (from 20.2m) and 2.5m @ 3.05g/t Au + 4,500ppm As + 1,137ppm Cu (from 279.5m). Other holes such as MM08 also cut several, narrow anomalous zones such as 0.6m @ 1.12g/t Au + 1,440ppm As + 0.209% Cu. Likewise, hole MM10, located approximately 1 km to the southwest of the target area, cut narrow, high grade mineralised structures including 0.3m @ 2.18g/t Au + >10,000ppm As + 2.6% Cu.
Two short boreholes, MM04 (120m) and MM05 (179m), were drilled immediately to the south of, but outside, the target area of interest, and were oriented to test the extensions of copper oxides in two north-south artisanal workings at depth. Hole MM04 was not assayed, and the limited intervals assayed in hole MM05 did not display significant gold-copper-arsenic values, confirming that the exposed copper mineralisation is confined in a carbonate buffer-zone within the top few meters.
The overall hydrothermal alteration patterns, together with the geochemical signatures (Cu-Au >> Zn-Pb), suggest a transition from a sub-epithermal carbonate-base-metal system to a porphyry copper-gold system at depth. It is likely that the chalcocite mineralisation is a result of supergene enrichment of primary chalcopyrite mineralisation contained within a sub-outcropping hematite-rich phyllic zone related to a possible porphyry copper-gold source at depth.
The Montezuma copper-gold-molybdenum project comprises approximately 45,000 Ha of 100% owned tenement. The Project is located along the main porphyry copper belt in northern Chile, commonly known as the Domeyko Cordillera, directly along the main West Fissure Fault System that controls several world-class copper deposits in the area, midway between the giant Chuquicamata (Codelco) and Centinela (Antofagasta Minerals / Marubeni Corporation) copper mining districts. The Project is centred approximately 20 km south of the important mining town of Calama. Access to the Project is excellent via a series of good dirt roads leading off from paved roads around Calama. Altitudes vary from approximately 2,600 m to around 3,100 m.