Altazor is a high sulfidation epithermal (HSE) gold project located in the prolifically mineralized Mio-Pliocene age mineral belt of Northern Chile. Altazor comprises approximately 33,230 ha of contiguous exploration claims and was staked by Mirasol as an outcome of the Company’s Atacama-Puna Generative program, which is targeting the discovery of large-scale gold, silver and copper deposits in the Tertiary age mineral belts of this region.
Altazor has favourable logistics, situated just 20 km south of 345 kV powerlines that follow International Highway Route 23, a paved road connecting northern Chile and Argentina. In common with other Mio-Pliocene mines and projects, Altazor is located at high altitudes of between 4000 and 5200 m; however, Altazor has good “drive up access” via an open valley and a network of easily passable gravel tracks.
On November 21, 2017, the Company announced that it signed an Option and Farm-in Agreement with Newcrest International Pty Limited (NCM), a subsidiary of Newcrest Mining Limited for the Altazor gold project in northern Chile. NCM has the right to acquire, in multiple stages, up to 75% of the Mirasol owned Altazor Project by completing US$ 10 million in exploration, and either delivering a positive bankable feasibility study or spending US$ 100 million in feasibility expenditure. Mirasol can then elect to solely fund its share of the residual feasibility and development costs to retain a 25% project equity position, or in exchange for an additional 5% project equity, require NCM to finance all costs through to production, with Mirasol retaining 20% of the project. If NCM elects to remain in the JV until the feasibility stage, it will pay to Mirasol US$ 1.8 million in staged option payments over 7 years. On November 12, 2018, Mirasol announced the NCM exercised its option to enter the Farm-in stage of the Altazor Agreement, making a US$500,000 payment to Mirasol. NCM has presented a budget of US$3.3 million for this season’s exploration program including a maiden drill program, subject to obtaining applicable permits and permissions.
Altazor is situated in an underexplored 860 km long section of the Mio-Pliocene age mineral belt located between Mirasol’s Gorbea Belt Projects and the historic, now idled, Choquelimpie HSE gold mine in far northern Chile. Mirasol believes the Chilean and Argentine section of the Mio-Pliocene age mineral belt is highly prospective for the discovery of new world class gold and silver deposits as exemplified by the recent discoveries of Salares Norte by Gold Fields and Barrick Gold’s Alturas HSE gold deposits.
The Altazor Project is centered on a district-scale zoned argillic to advanced argillic alteration system hosted by a dacitic to andesitic volcanic complex, that is crosscut by multiphase, strongly altered phreatic and hydrothermal breccia systems. A large proportion of the Altazor project is capped by laterally extensive, but relatively thin, unaltered post mineral volcanics, that conceal the full dimensions of the alteration, estimated to be developed over an area of >75 sq kms..
All results from last season’s exploration program have been received. This includes long lead time “Corescan”* alteration analysis of soils and radiometric age dates as well as results from a 1,035 line-km ground magnetic survey, geological mapping and rock chip sampling over an area of 128 sq. km, a 2,030 sample, low detection limit soil grid covering 85.6 sq. km, and a 66.9 line-km CSAMT resistivity geophysical survey.
Integrated analysis of the combined data sets shows Altazor to be a district-scale, zoned alteration system, preserved at a level that could conceal HSE gold deposits beneath a “barren” steam heated cap rocks and post mineral cover, as has been the case at recent multimillion ounce discoveries elsewhere in the Mio-Pliocene mineral belt in Chile.
NCM and Mirasol have received results from three K-Ar alunite alteration age dates from Altazor that range between 7.3 to 7.8Ma. An additional K-Ar age determination on biotite for the post mineral volcanics has returned a younger age of 5.8Ma. The alteration ages for Altazor fall within the key mineralization window of 6.2 to 13.1 Ma that “brackets” the formation of the giant Mio-Pliocene age HSE gold deposits in the El Indio Belt (EIB) of Chile and Argentina. Bracketing of the Altazor alteration age within the EIB mineralization ages confirms the Altazor system formed during this key period for gold deposit formation and as such, may have the potential of being a productive precious metal system.
Alteration and breccias outcrop intermittently along a 15 km long NE-oriented range front that is interpreted as a series of large fault scarps. The 207 sq km ground magnetic survey completed over the project, shows a series of large magnetic depletion zones, correlating with the mapped areas of alteration, that are separated by the magnetically distinct post alteration volcanics. It is interpreted that the post alteration volcanics partially “mask” the magnetic depletion signature of the underlying alteration, suggesting the Altazor system may cover a much larger area and be open to the south into the new claims recently staked by the NCM and Mirasol.
Au+Ag mineralization in HSE deposits is invariably associated with bodies of intense silicification and brecciation. CSAMT geophysics has been successfully used in recent significant HSE gold discoveries as an exploration methodology to target concealed high intensity resistivity anomalies, that subsequent drill testing confirmed to be vuggy silica and silicified breccia bodies hosting gold mineralization at these projects. At Altazor, in the central part of the alteration system, 66.9 line-km of CSAMT was surveyed on 400 and 800 m line spacing and delineated a series of concealed and predominantly open ended, intense resistivity highs (7,500 to >30,000 Ohm-m) anomalies at the Alunita, Sulfuros and Pirofilita prospects.
Geochemistry from 2,030 soil samples collected on an 85.6 sq. km soil grid using low, ppb detection limit, four acid digest, multielement analysis show subtle element patterns in “geochemically barren” steam heated and advanced argillic altered cap rock (Figure 2). Integrated analysis of this data has mapped low, ppb level Au (peak assay 131 ppb) with strongly anomalous Ag+Sb+Te+As that vector toward the SW into an area of concealed high intensity CSAMT resistivity anomalies at the Alunita and Sulfuros prospects. The Pirofilita prospect is characterized by soils that are strongly anomalous in Ag (local peak values of up to 22.3 and 54 ppm) and Sb, with low level Au, spatially coincident with outcropping intensely silicified breccias and concealed, highly resistive CSAMT anomalies.
Systematic analysis of all soil samples with Corescan provided a powerful additional dataset that was used to map district-scale zonation in alteration mineral assemblages and was combined with the soil geochemical analysis to map spatial variation in indicator element ratios in alunite chemistry (Alunite Geochemical Vectors).
Alteration mineral assemblages and alunite geochemistry that emerged from this analysis are important new methodologies for exploring in large high-level alteration systems to target covered mineralization bodies. At Altazor these results vector to the SW, corroborating the soil geochemistry vectors and further highlighting the concealed CSAMT resistivity anomalies as priority drill targets.
The 2017/18 Altazor exploration results highlight the large areal extent of the alteration system at the project that will require several seasons to complete a first pass evaluation. The integrated leading-edge technologies applied during the first season’s exploration, have identified multiple compelling large-scale drill targets in three principal prospects that have alteration, geochemical and geophysical characteristics in common with the predrill target signatures of Salares Norte and other recent HSE gold discoveries.
Analysis of the Altazor data sets outlines alteration mineral composition variation and low detection limit soil geochemistry anomalies, highlighting predictive patterns that vector towards a series of covered and predominantly open-ended, very resistive (7,500 to >30,000 Ohm-m) CSAMT geophysical anomalies at the Alunita, Sulfuros and Pirofilita prospects. These anomalies define large-scale targets that have the form, dimensions and intensity of resistivity response that could indicate a series of silicified breccia and or vuggy silica bodies. The association of Altazor mineral chemistry and soil geochemistry vectors, and CSAMT resistivity anomalies define a series of high priority conceptual targets for large scale HSE gold mineralization**, that will be the focus of the planned 2018/2019 maiden drill campaign.
* Corescan’s Hyperspectral Imager integrates high resolution reflectance spectroscopy (0.5mm), visual imagery (0.05mm) to map mineralogy and mineral chemistry.
** Azevedo, F., Brewer, N., Santos, A., Huete Verdugo, D., Baumgartner, R., Roncal, L., Trueman, A. & Foley, A. (2015). The discovery and geology of the Salares Norte epithermal gold-silver deposit, northern Chile. In NewGenGold 2015 (p145-157). Perth, Australia.