Exploring for a Tier 1 Gold System in the Rochford Gold District
Black Hills, South Dakota, U.S.A
In late 2012, Mineral Mountain’s experienced technical team recognized that the 70 km long Homestake Gold Trend located in the Black Hills of South Dakota, hosting the world’s deepest and richest iron formation hosted gold deposits and one of the largest gold producers in North American history having produced over 40 million ounces of high grade gold, was largely unexplored since 1997. It was also recognized that the Rochford District, situated only 20 km south of the Homestake Mine, despite the great geological similarities and the compelling evidence for gold mineralization, this portion of the Homestake Gold Trend was overlooked by explorers. The close similarities between the Homestake Mine and the Rochford District in host rock composition, structural style, metamorphic grade, gold mineralization and the Company’s extensive historical database clearly suggest that the district has the potential to contain a wold class Tier 1 gold system.
Proof of Concept
Comparison of 1980s-1990s Era Gold Drilling Intersections in the Rochford District Iron Formation Between Discoveries by Homestake Mining 15-Ledge and Homestake North Discoveries
Homestake 15 Ledge Discovery Program
- Approximately 83 drill holes existed in 15-Ledge synclinoral fold structure (the only major synclinal structure not known to host orebodies in the Homestake Mine environment), with no known ore-grade intersections, before Homestake began the “15 Ledge” program.
- Program was based on the projection of favorable structure & stratigraphy down plunge from existing sub-ore grade, sporadic Au mineralization in the upper 15-Ledge fold structure.
- A systematic 36-hole drill program tested the target area, form underground drill setups spaced initially several 100s of meters apart. Best result from this phase was ~1 meter @ 4.6 g/t Au, but many lower-level Au concentrations (high 10s to 100s ppb), increased arsenopyrite and late-stage quartz veins with chlorite selvages were used to define vectors toward Au mineralization.
- Resumption of a second phase of drilling on 50m to 100m step-outs from the modest mineralization encountered in the initial program (above), after modelling the data from first 36 holes, resulted in the intersection of 25 g/t Au over 10 m, considered the discovery hole for 15-Ledge.
- 15-Ledge Ore Zone (late 1980’s) was the first new ore ledge discovered in Homestake Mine since 1969 and contained ≈ 1,000,000 ounces Au.
Homestake North(Sheeptail Gulch) Discovery Program
- Sheeptail Gulch area is 3 miles north of Homestake mine.
- Target was intersection of northerly-striking steep deformation zone with NNW striking F2-folds in Homestake Fm. on the west side of the Poorman Anticlinorium.
- This represented a bold move, since all previous exploration for over 100 years had been down-plunge onthe synclinoral structures on the east side of the Poorman Anticlinorium, in the Homestake Mine system.
- Deep holes, drilled from surface from 3 setups, spaced several 100s of meters apart, with 6 wedges from each trunk hole, resulted in 200 penetrations of folded Homestake Fm.
- Only one of these drill penetrations had significant Au, in the ≈ 1 g/t Au range
- Follow-up drilling at 50m to 100m step-outs, in proximity to this intersection, resulted in 3 drill intersections ranging from 3 to 30 g/t Au, in different parts of the same fold structure, considered the Homestake North discovery holes.
Rochford Gold Project Priority Gold Targets
- Mineral Mountain’s proposed drilling program is based on the concepts, proven successful at Homestake, that Ledge-type gold targets are controlled by the intersection of steep deformation zones with iron formation in structurally thickened F2 synclinoral fold axes.
- Although Mineral Mountain has not drilled targets to date in the Rochford district, the proposed program is based on the same proven, systematic exploration methodology as used by Homestake, and summarized below:
- Target the intersection of major deformation zones with structurally thickened iron formation in synclinoral settings.
- Vector toward ore using increasing abundance of late-stage quartz veining with thick chlorite vein selvages, increasing arsenopyrite, and increased gold concentrations locally.
- Follow-up significant (~gram to multi-gram) Au intersections with closer-spaced (~50-100m step-outs) drilling.
- There are a number of clear opportunities in Rochford District, in the right geological setting (thickened synclinoral iron formation fold structures, cut by sub-parallel deformation zones) that have not been systematically followed up. Each opportunity has early-stage gold intersections as good, or better those that Homestake followed-up to make their 15 Ledge and Homestake North Discoveries:
- South Cochrane Trend Example:
- Non-NI43-101-Complaint inferred resource of 268,000 oz @ 6.34 g/t Au. Numerous high-grade drill intercepts are open down plunge onto MMV Claims (refer to 2016-11-07 MMV PowerPoint Slides #17-21 on Cochrane and Cochrane South Trend, and especially Slide #22 on the Cochrane – Homestake 9-Ledge Comparison.
- Standby Trend Examples:
- High grade intersections in near Standby Mine (BLG-UG3 = 12.19m @ 4.61 g/t Au) and SM87-3A = 3.05m @ 10.29 g/t Au (Homestake Mining, 1987) 1500 m down-plunge from Standby Mine, there are other significant intersections between these DDHs (refer to 2016-11-07 MMV PowerPoint Slides #12-16 on Standby Trend, particularly the Standby Long Section Slide #14).
- WMC Bloody Gulch Example:
- A deep trunk hole with 2 splays in the Bloody Gulch area south of Standby (intersected 1.15m @ 1.19 g/t Au & 1.35m @1.17 g/t Au within a broader interval of weakly anomalous Au in quartz-veined, chlorite-quartz-pyrrhotite altered iron formation).
- Lookout Mine Trend
- 2 DDHs down-plunge from the Lookout Mine (RV-95-1 intersected 0.58m @ 4.22 g/t Au within a broader interval of 1.65m @ 2.06 g/t Au; RV-95-2 intersected 1.4m @ 4.92 g/t Au within a broader 6m Au-anomalous zone with attendant arsenopyrite and well-developed chlorite selvages on quartz veins (refer to 2016-11-07 MMV PowerPoint Slides #12 for location of Lookout Trend).
- All of the above examples illustrate target trends in the Rochford District that are open down-plunge from the historical gold intersections (and, in the case of the Standby Mine Trend, also have sufficient space, 750m, between some of the known intersections) and are capable of hosting a multi-million ounce Homestake-Style Ore Ledge or Ledges.
Notably, placer gold production from Rapid Creek and Castle Creek, which drain the Rochford District, is estimated at perhaps as much as several hundred thousand troy ounces (Parker, 1966). This suggests that while modestly significant gold was eroded, perhaps from the Standby and Cochrane mineralization and other smaller occurrences, the above target trend examples more likely represent Upper Tail positions, with most gold potential still present at depth, rather than Lower Tail positions, in which case vastly large quantities of placer gold might be expected to have been produced from eroded Ore Ledge Centroid positions. This case is also suggested by the similar metamorphic grades of the rocks at Homestake and Rochford, suggesting similar levels of exposure. At Homestake, only the Main Ledge and Caledonia Ledge outcropped to the Precambrian erosional surface.
Why is the Rochford District Unexplored??
Homestake focused on finding new reserves from about 1983-1995. Homestake knew what they were doing, and they spent their exploration dollars, or encouraged their JV partner WMC Resources (“Western Mining”) to do so, primarily in two places in the Black Hills, outside the Homestake Mine:
- The Maitland to Sheeptail Gulch area, northwest of the Homestake Mine, where they made the “North Homestake Discovery”.
- The Rochford District (Bayley, 1972), specifically in the Standby area, as detailed in some of the gold intersections described in the previous section on the Rochford District.
- Additionally, WMC, in JV with Homestake, and in consultation with Homestake, drilled in the Bloody Gulch Trend and Lookout Mine Trends, as also noted in the previous section.
- Homestake realized that exploration for these targets required perseverance, and they had not finished exploration at Rochford by any means. In general, Homestake’s persistence in the region paid off in two discoveries (15 Ledge & Homestake North) within, and north, of the Homestake Mine (Caddey and others, 1991; 1991a). However, very low gold process (≈$200-$300 US range), deep more expensive production at the Homestake Mine, and the mandate from Homestake Management to quickly find 9-Ledge scale (~5-10M ounce) discoveries, resulted in Homestake’s curtailing exploration and eventually closing the Homestake Mine in 2001.
- Newmont dropped Cochrane area exploration in the Rochford District in the 1990s, despite encouraging drilling results, because they did not have sufficient land down-plunge on the Cochrane target. They could see that the #1 target at Cochrane was plunging to the south off the patented ground onto ground that Mineral Mountain Resources now controls. Newmont tried to make a deal on those claims, owned by Rutherford Day (“Bobcat Properties”) at the time, but WMC out-negotiated them. If Newmont had gotten the ground, they had planned more work drilling in that direction.
- WMC left the joint venture with Homestake in 1995, despite technical success, particularly at the Lookout Mine Target, that exceeded Homestake’s initial Au intersections compared to the 15-Ledge and North Homestake projects, because of a need to fund their Meliadine program in Nunavut (resulting, incidentally, in the discovery of the ~3.3M ounce Meliadine Gold Deposits, by following up a similar targeting strategy as at Homestake and Rochford.)