The Copperwood project is Highland’s 100%-owned. The Copperwood Project consists of four metallic and non-metallic mineral leases. Each lease was executed by Copperwood Resources Inc., formerly known as Orvana Resources US Corp., a wholly owned subsidiary of Highland.
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Summary:
The Copperwood Project is situated on the flank of the 2,200 km long Mesoproterozoic mid-continent rift system of North America and is hosted in the Nonesuch Formation; a package of lacustrine and fluvial sediments, which form part of the Oronto Group post-rifting basin fill. Mineralization is hosted within two sedimentary sequences termed the Lower Copper Bearing Sequence (“LCBS”) and Upper Copper Bearing Sequence (“UCBS”) at the base of the Nonesuch Formation.
Deposit Types
The mineralization at Copperwood has been interpreted as a sediment-hosted stratiform copper deposit of the reduced facies class.
Sediment-hosted stratiform copper deposits consist of copper and copper-iron sulphide minerals hosted by siliciclastic or dolomitic rocks in which a relatively thin copper-bearing zone is mostly conformable with stratification of the host sedimentary rocks. Copper in chalcocite occurs as disseminations and seams along bedding planes. Chalcocite is the only observed copper sulphide bearing mineral present at Copperwood.
Mineralization
The Copperwood and Satellite Deposits are situated on the limbs of the Presque Isle Syncline within the Nonesuch Formation. The Nonesuch Formation contains two mineralized sequences, one located at the base (LCBS), and another located stratigraphically higher (UCBS), separated by poorly mineralized sediments from 0.5 to 6.0 m thick.
The LCBS is composed of the Domino, Red Massive and the Gray Laminated units. The Domino unit is the principal copper host at Copperwood and is characterized by black shale with a mean thickness of 1.6 m. The Red Massive sub-unit comprises siltstone to sandstone and has a mean thickness of 0.3 m. The Gray Laminated sub-unit is a gray laminated siltstone and has a mean thickness of 1.0 m.
The UCBS is composed of the Upper Transition, Thinly, Brown Massive and Upper Zone of Values units. The Upper Transition unit comprises thinly bedded siltstone to sandstone and black shale with a mean thickness of 1.0 m. The Thinly unit is characterized by black shale with a mean thickness of 0.1 m. The Brown Massive unit is characterized by a brownish-red siltstone with a mean thickness of 1.1 m and one- to two-centimeter-thick calcareous nodules. The Upper Zone of Values unit is composed of laminated, greenish black, shaley siltstone with a mean thickness of 0.5 m. The UCBS is separated from the LCBS by thinly to medium-bedded red siltstone, grey siltstone, and sandstone. The thickness between the UCBS and the LCBS gradually decreases from 6.0 m in the western part of the Deposit to 0.5 m in the eastern part of the Deposit.
The LCBS and UCBS at Copperwood have been delineated by drilling over an area of approximately 5,600 m east-west and 1,700 m north-south. The Copperwood and Satellite Deposits are hosted within the limbs of the broad, gently northwest-plunging Presque Isle Syncline. The LCBS dips gently and subcrops beneath 20 to 35 m of unconsolidated glacial sediments along the southern edge of the Copperwood Project area.
The Domino is the main mineralized subunit, averaging 1.6 m in thickness, but thinning to about 0.5 m on the eastern edge of the Copperwood Deposit. Copper assays at Copperwood are remarkably consistent within individual units with mean copper grades of 2.58 wt.%, 0.39 wt.%, and 1.32 wt.% for the Domino, Red Massive and Grey Laminated subunits, respectively. The Red Laminated demonstrates a localized 1% increase in copper grades occurring at the base of the unit adjacent to the Grey Laminated. Silver is also present, with mean grades of 5.5 g/t.
Chalcocite is the only observed copper sulfide-bearing mineral at Copperwood, occurring principally as disseminations within shale and siltstone. Individual disseminated grains of chalcocite are most commonly very fine-grained, approximately 5 to 50 microns (“µ”) in diameter. Chalcocite occurs as free grains and as complex grains where it appears to have replaced pyrite grains, as evidenced by remnant patchy domains of an iron oxide mineral (probably hematite). In the highest-grade samples, located in the top 0.3 m of Domino subunit, chalcocite occurs as layers that are parallel to laminations in the rock. These layers are usually less than 2 mm thick. Occasionally, ovoids of chalcocite occur that are up to 3 mm in their long axis. They possibly resulted from the replacement of organic carbon.
There is an overall negative correlation with the degree of oxidation of the host rock within the LCBS and the abundance of chalcocite within the LCBS. The dark-grey to grey colored Domino subunit has the highest copper grades; the medium to light-grey-colored Grey Laminated has medium copper grades; and the red-brown colored Red Massive has distinctly the lowest copper grades.
Grade profiles for each of the LCBS units show that there is a natural break in the grade profile, at approximately 1 wt.% copper. The 1 wt.% copper grade is a natural cut-off and is extensively used in Zambian and other African sediment-hosted copper deposits, where most intercepts grade a few tenths of a percent copper above or below the mineralized interval and well over 1 wt.% copper inside the mineralized interval.
The UCBS hosts the same style of chalcocite mineralization as the LCBS but contains trace to no chalcocite mineralization in the western, thicker part of the deposit. The copper grade gradually increases towards the center of the Presque Isle Syncline, Section 6 contains an UCBS grade of 0.5 to 0.8 wt.% copper. The UCBS becomes more mineralized in Section 5 and has a copper grade greater than 1.0 wt.% in the eastern half of the section, where the thickness of the UCBS ranges from 2.5 to 3.2 m. Here the copper grades are greater than 1.5 wt.%, 3.0 wt.%, 0.3 wt.%, and 0.9 wt.% for the Upper Transition, Thinly, Brown Massive, and Upper Zone of Values subunits, respectively. The Upper Transition and Thinly units are of economic interest and were the focus of recent drilling programs.
Although the average grades of silver in the Domino and Grey Laminated are of lower economic importance (4-6 g Ag/t), the spatial distribution of silver grades is highly variable. A sub-population of higher-grade silver assays (up to 108 g Ag/t) are present in the Domino to the north of the Copperwood Deposit, located within the keel of the syncline.