Copperstone Resources AB states that an Exploration Target potential of 150-210 million tons at a grade of 0.25-0.45% copper has been predicted by Micon International Co LTD (UK) for the Granliden area of the project. This potential is in line with the latest guidance and is based on an autonomous analysis of exploration drilling results mainly from the drill campaign performed by Copperstone in 2018.
Furthermore, Copperstone has also received a PERC 2017 compliant Mineral Resource Statement from Micon for the shallow copper mineralization at both Svartliden and Granliden Hill. In total, 26 million tons of Inferred Mineral Resource at a grade of approximately 0.43% copper has been established, with realistic prospects for subsequent economic extraction at stated modeling factors.
In 2018, the Granliden area of the project has been explored with 10 NQ2 drillholes (total 7,615 m). Drillholes were initially planned to probe new geophysical anomalies derived from Ground Magnetic and NSAMT field surveys done in 2017, and to construct a better picture of the geological model and style of copper mineralization. Major assay results received between January 2018 and August 2018 have already been publicized by the Copperstone. Two drill holes (COS18359 and COS18364) both returned substantial copper grades over broad intervals showing that mineralization is present at depth well under and to the east of Granliden Hill. Other drill holes in this campaign have also established copper mineralization and the detection of formerly unidentified granitic intrusives that may be related to the mineralization event(s). These hopeful results have led to the probability to currently update the Exploration Target potential of the property.
In 2014 and before Copperstone had drilled any boreholes on the property, it specified that an Exploration Target of 60-100 million tons at grades of approximately 1% copper may exist over the whole property. So as to consolidate all separate historical and new drill hole results along with a better geological understanding, and to illustrate the important discovery potential in Granliden area, Copperstone requested an autonomous assessment of the Exploration Target potential by Micon.
Wireframes of copper mineralization in the Granliden area were built in 3D space using all drillhole results in that area. Not including any mineral resources, there is an estimated potential of 150-210 million tons of mineralization at grades of 0.25-0.45% copper. Mineralization is seen in all directions. Presently, the spacing of drill holes outside of the mineral resource wireframes is very wide to produce any further code-compliant mineral resources. There is also no guarantee that additional exploration drilling will establish any more mineral resources within or beyond the existing Exploration Target potential. However, Copperstone is self-assured that additional exploration is necessary to explore this potential.
In April 2016 Copperstone reported a JORC-compliant Inferred Mineral Resource of 5.4 million tons at an approximate grade of 1% copper for Granliden Hill and Granliden South. This estimate was given by Geovista AB and was based on six drillholes completed by Copperstone back then besides the historical drilling in those areas. Since then it has conducted more geological logging and infill sampling of historic drill cores, and down-hole Optical Televiewer probing in available drillholes to produce structural/trend data. From a review of all the new exploration data, an enhanced estimation of copper mineralization resources has currently been done by Micon.
To form wireframes for mineral resource estimation, a cut-off of 0.135% copper, a capping of 3.69% copper and a maximum internal waste intercept of <10 m was applied by Micon. In situ density is based on the examination of sulfur values with regard to laboratory density results produced historically and verified recently through check measurements by Copperstone. Block modeling was done using Inverse Distance Weighted to Power 3 (IDW3) estimation method.
To adhere to the rules for declaration of Mineral Resources as stipulated by the PERC code (2017) it is essential to prove that Inferred Resources have realistic prospects for economic extraction using declared mining criteria. Whittle modeling was used by Micon to produce pit-optimized Inferred Resources at a mining cut-off of 0.1% copper at a metal price of 6,200 USD/ton.
The Inferred Mineral Resource estimation results by Micon are given below:
- Granliden: 16.92 mt at 0.44% copper and 3.65 g/ton silver
- Svartliden: 9.43 mt at 0.42% copper, 9.76 g/ton silver, 0.12 g/ton gold and 0.34% zinc
Altogether, the shallow open pit Inferred Mineral Resources for the property has increased greatly to approximately 26 mt with an average grade of approximately 0.43% copper and 5.90 g/ton silver. This resource estimate is besides the 150-210 mt Exploration Target presently declared for the Granliden area.
The 9.4 mt Inferred Mineral Resource at Svartliden is the first publication for this copper-zinc mineralization zone. All mineralization found so far is held within or close to the pit-optimized Inferred Mineral Resource wireframes. There is a low resistivity anomaly coincident with a magnetic anomaly directly under this resource. Deeper exploration drilling is needed to test out the cause of these geophysical anomalies and search for any additional resource potential below. However, there can be no assurance that additional drilling will locate any extra mineral resources at Svartliden.
We have worked hard and with great belief. Today this is a great outcome for our project. I have seen down the years of my work that a large scale complex hydrothermal system exists here. Mineralisation is extensive, zoned and related to structurally controlled intrusives I believe. We have used the term porphyry-style to encompass our views and lay a foundation for exploration methodology and scale in the future. This year our first large drill campaign of 10 deep drill holes on the property has shown many new geological aspects, and tested out a few ideas. We found good mineralisation and established Copperstone as one of the main exploration companies based and operating in Sweden. This we are proud of and this effort has set the scene for future success. I have no doubt that we are on the right path, and with further drilling this massive potential can be realised for Copperstone.
I’m thrilled that our new estimate of the 150-210 mt exploration target potential at Granliden alone has out-performed our first pre-drill estimates for the property. Right now further drillholes are required to test this massive target in the Granliden hill area. Here onwards the new wireframes can be a guide to value-creation through well-placed drill holes. Besides expanding the net of exploration drill holes beyond the wireframes, building of a gridded network of drill holes spaced close enough is key to growing and improving the resources of this property. This approach will bring great rewards I’m sure. Naturally, I believe that subsequent resource estimates will grow in size and confidence, and in time the Company can look forward to those returns. Coppertone is a unique and exciting opportunity, and this has been a pleasure to develop thus far.
Chris McKnight, CEO, Copperstone Resources