Gran Colombia Gold provides exploration update
Published by Jessica Casey,
Global Mining Review,
Gran Colombia Gold Corp. has announced that the first eight step-out diamond drill holes at the Vera brownfield target in its Segovia mining title have resulted in multiple high-grade gold and silver intercepts, including:
- 96.68 g/t gold (Au) and 423.7 g/t silver (Ag) over 0.49 m on the Lluvias Vein (VER-ES-006).
- 46.54 g/t Au and 365 g/t Ag over 0.34 m on the Lluvias Vein (VER-ES-005).
- 5.48 g/t Au and 212.1 g/t Ag over 0.64 m on the Lluvias Vein (VER-ES-003).
The diamond drill holes at Vera, totalling 2223 m, were carried out from surface as part of the company’s brownfield drilling programme which commenced in October 2020 aimed at testing the down-dip continuity of the historical Vera mine, a past-producing mine operated by Frontino Gold Mines Ltd (FGM) from 1940 until 1988. The Vera vein is one of 24 known veins in the Segovia mining title that Gran Colombia is not currently mining.
Serafino Iacono, Executive Chairman of Gran Colombia, commented: “We are very encouraged by these early drilling results at Vera which provide a clear indication that mineralisation is still open at depth. This is a very exciting time for Gran Colombia, as we continue to explore our high-grade producing mines and expand our exploration efforts to include regional brownfield targets. The exploration team has done an outstanding job over the last several years as we have continued to replace and replenish our resource base and reserves at our mines. Now the team is ready to take on a strategic, expanded brownfield exploration programme, targeting new resources that will utilise our current infrastructure and capacity, leading to production growth and mine life extension at Segovia. We are confident that our exploration campaign will continue to be a key value driver for Gran Colombia as we move forward.”
Highlights of the Vera Drill Programme
- The Vera brownfield target is located east of the Sandra K – Cogote Vein System and represents one of the highest priority targets in the company’s brownfield drilling programme at Segovia.
- Following a 3D geological and structural modelling exercise incorporating a compilation of old channel sampling and mining data along with a new detailed geological-structural survey, an initial diamond drilling programme totalling 3500 m in 12 holes was designed for the Vera brownfield target. This is aimed at testing the down-plunge continuity of the main orebody mined in the past and the extension of a potential NE plunging ore-shoot occurring in the southern sector of the historical mine, currently being mined by artisanal miners under contract with the company.
- The brownfield drilling programme at Vera commenced in early October 2020 with one diamond drill rig operating from two purpose-built surface drill stations. Approximately 63% of the total drilling programme was completed by the end of January in the eight drill holes reported in this press release. The remaining four drill holes (approximately 1300 m) will be completed by the end of March 2021.
- Drilling has confirmed a new model for the Vera vein which was built based on historical drill hole intercepts, new structural data, chip channel data and fieldwork. This new model incorporates a post-mineralisation NW striking dextral oblique-reverse fault that dips to the NE. This was not previously identified by FGM, which interpreted that there were two sub-parallel quartz veins named Vera and Lluvias, the latter in the hanging-wall of the Vera vein. The intersections to date of the current drill programme confirm the presence of the interpreted fault and the relative displacement along it, and support the model that the Vera and Lluvias veins are the same vein, with the Lluvias vein occurring in the upthrown fault block.
- Gran Colombia’s drilling programme was successful in confirming the continuity of the high-grade gold and silver mineralisation in the upthrown fault block, below the deepest level of the historical mine.
- The presence of high silver grades at Vera confirms the metal zoning pattern and polarity that characterise the entire eastern sector of the Segovia RPP-140 mining title, shown by a reversal of the gold (Au)/silver (Ag) ratios from Sandra K to Guia Antigua.
- The style of mineralisation of the intersections drilled so far is characterised by narrow veins hosting two main stages of mineralisation. ‘Stage 1’ is represented by milky quartz and pyrite and galena forming nests, while ‘Stage 2’ is characterised by grey quartz and pyrite intergrown with galena and sphalerite along with minor amounts of silver sulfosalts (possibly proustite and/or pyrargyrite). The veins are enveloped by a narrow halo of sericitic alteration.
FGM developed the Vera mine on six levels, the longest (Level 2) with an approximate length of 715 m. Gold and silver mineralisation at Vera is contained predominantly within a N-S to NNE-SSW trending massive white quartz vein dipping moderately (35 – 40°) to the east, with an average width of 1 m. The vein is hosted by granodiorite and diorite of the Segovia Batholith. The main ore-shoot mined by FGM at the northernmost end of the mine plunges NE, is approximately 200 m wide and had a historical average grade of 28 g/t Au. This trend is consistent with the general plunge of the ore shoots within RPP-140. Historical records report 16 507 t with 6.5 g/t of Au as proven reserves and 24 745 t with 28.1 g/t Au as probable reserves as disclosed in a private report by FGM in 1981. This mineral reserve estimate is a historical estimate as defined in National Instrument 43-101. The mineral reserve categories for this estimate predate the CIM standards and definitions for mineral reserve classification and therefore do not conform with the current definitions of mineral reserves as stated in NI 43-101. The estimates are of unknown reliability but are included for purposes of depicting the history of the property. A qualified person has not done sufficient work to classify the historical estimate as current mineral reserves. The historical estimate is not being treated as current mineral reserves.
Overview of Segovia Operations drill programme
Gran Colombia also announced that it plans to drill a total of approximately 60 000 m at its Segovia Operations in 2021 at a total cost of approximately US$14 million to carry out its ongoing in-mine and near-mine drill programme at its four operating mines and ramping up its exploration programme aimed at testing its highest priority brownfield targets.
Gran Colombia currently has six diamond drill rigs in operation at Segovia, with two rigs carrying out resource definition within the underground developments of the Sandra K and El Silencio mines, one rig operating from underground at the Providencia mine testing the continuity of the Providencia vein system to the west, one rig operating from Level 3 of the Sandra K mine targeting the down-plunge extension of the southern ore-shoot of the El Silencio mine, one rig testing from surface the westernmost end of the Providencia mine, and one rig at Vera.
In-mine and near-mine drill ppogramme
Gran Colombia’s 2020 drilling programme continued to provide outstanding results, providing further confirmation that the Segovia Operations are a world-class gold system. The 2020 drilling programme led to the discovery of a third high-grade vein at depth in the El Silencio Mine, the discovery of a new orebody at Level 14 in the Providencia mine which is being developed and remains open at depth, confirmation that the mineralisation at the northernmost end of the Sandra K mine is still open along strike and at depth, and the presence of additional high-grade mineralisation well below the existing underground mine development at the Carla mine. The company expects to have updated mineral reserve and resource estimates incorporating the results of its 2020 drilling programme at the end of March 2021.
The 2021 in-mine and near-mine drill programme at the Segovia Operations, which is already underway, will total approximately 40 000 m of step-out and in-fill diamond drilling from purpose-built underground and surface drilling stations at the company’s four operating mines, distributed as follows:
- Approximately 16 200 m at the El Silencio mine.
- 12 600 m at the Sandra K mine.
- 9100 m at the Providencia mine.
- 2100 m at the Carla mine.
In-mine and near-mine drilling will be focused on replacing the 2021 mining production and organic growth through resource and reserve expansion at the company’s core operating mines. Total budget for this drilling campaign is expected to total approximately US$10 million.
Brownfield exploration programme
The Segovia RPP-140 mining title hosts more than 27 know veins and more than 50 small mining workings. During 2020, Gran Colombia’s target generation exploration team carried out a prospectivity analysis of a large geological dataset focused on reprocessing and reinterpreting the exploration data contained in a data room inherited from FGM. This work culminated in the generation of brownfield exploration targets, interpreted as areas ranked more likely to be prospective for gold mineralisation than others based on geological factors. As a result of this ranking exercise, the entire Segovia RPP-140 mining title was divided into 11 domains based on geological, structural and mineralisation features, which has led to an exploration programme that will be balanced between conceptual greenfield and brownfield targets to be tested by diamond drilling.
The 2021 brownfield exploration programme at Segovia comprises a multi-phase fieldwork programme for each of the high-priority exploration targets, namely: Vera (ongoing), Cristales, Marmajito and San Nicolas. Planned exploration work includes unmanned aerial system magnetic and radiometric surveys, underground and surface mapping, and possibly induced polarisation surveying. A total of approximately 20 000 m of exploration and step-out drilling has been planned, of which 6300 m will be drilled at Vera (additional to the current programme), 7400 m at Cristales, 4200 m at Marmajito and 2100 m at San Nicolas. The total budget for these programmes is approximately US$4 million. Fieldwork, including drilling, will be spread out throughout the year with Cristales expected to begin in 2Q21 and Marmajito and San Nicolas to follow in 2H21.
Read the article online at: https://www.globalminingreview.com/exploration-development/23022021/gran-colombia-gold-provides-exploration-update/
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