Bunker Hill provides exploration update and announces maiden resource
TORONTO, CANADA — Bunker Hill Mining Corp is pleased to report that it has commenced its first high-grade silver focused exploration campaign at its Bunker Hill Mine located in Idaho’s Silver Valley. The exploration campaign is being supported by the enhanced geological understanding gained following the recently completed digitization and 3D modeling of historic geological data which confirmed numerous high-grade silver exploration targets.
This first high-grade silver exploration program will consist of 15,000 feet of diamond drilling from surface and underground focused on targets in the upper levels of the mine located in close proximity to existing infrastructure.
Sam Ash, CEO of Bunker Hill Mining, stated:
“We are excited to commence our high-grade silver focused drilling campaign as it is the culmination of six months of forensic work, as we have analyzed over a 95-years of historical mine data to identify and prioritize our targets. Following this analysis, we made silver exploration our primary focus given the potential to unlock significant value.”
In addition, Bunker Hill is pleased to report that it has successfully verified the mineralization on which the historic reserve was tabulated, based on the drilling, sampling and data review campaign conducted in Q2-2020 prior to its strategic shift to high grade silver exploration. A total maiden Inferred resource of 9Mt has been delineated, thereby boosting confidence in the quality of historical data.
Commenting on the maiden Inferred resource, Sam Ash, CEO of Bunker Hill Mining, added: “We are pleased to have outlined this maiden resource as it boosts confidence in our ability to delineate resources in a cost-effective manner by leveraging historical mine data. While high grade silver remains our main focus, this zinc-rich resource offers strategic optionality.”
ABOUT THE BUNKER HILL GEOLOGY
The Bunker Hill Mine has exploited a series of silver-lead-zinc veins hosted in quartzites of the Upper Revett formation, which is a part of the Belt Supergroup, a thick package of Precambrian siliciclastic sedimentary rocks deposited in a continental-scale, low-energy basin. The Upper Revett formation consists of interbedded hard, competent quartzite units and less competent argillite and siltite units.
Historic mining at Bunker Hill exploited distinct types of vein systems with different orientations, mineralogies and structural controls. The earlier veins, referred to as Bluebird type veins, strike WNW to NW, dip to the SW and contain sphalerite-pyrite-siderite mineralization. Younger predominately northeast to east-west striking veins containing argentiferous galena and quartz mineralization that dip southerly are collectively called silver-lead veins. The largest historically mined material at Bunker Hill with the highest contained metal values formed where the younger silver-lead veins intersected the earlier more sideritic Bluebird veins resulting in a hybrid type of mineralization. Although hybrid shoots formed within Bluebird vein zones, the most important hybrid shoots are mainly silver — lead mineralized bodies, even though some hybrid veins have important quantities of zinc.
Over the course of several years in the late 1970s, a dedicated team of geologists conducted ground-breaking research on the material controls of the veins. The research for the first time defined distinct stratigraphic horizons in the upper Revett formation that could be correlated and mapped over distances of thousands of feet. The research showed that minerlized shoots occur mainly in the hard, competent quartzitic stratigraphic units in the Upper Revett formation. One of the most important breakthroughs was that the research established that the veins formed in association with distinct regional folding events. As regional metamorphism transitioned from ductile to brittle deformation, folding and vein formation ceased, and major faults developed that segmented and offset some of the mineralized shoots. The 1970s research ended shortly before the mine closed, and the new concepts were never fully applied to exploration. Some of the geologists from the original research team, who currently operate as DJ Consulting, are working with the Company to utilize insights from the 1970s and ongoing research to identify new exploration vectors and targets.
Following the change in management in early 2020, a digitisation program was launched in Q2-2020 to leverage the historical mine data collected over a 95-year period to identify and prioritize high grade silver targets. Data has been inputted from more than 180,000 meters of drilling from 3,500 historic drill-holes and hundreds of detailed historic mine geology maps capturing all major faults and veins, alterations, mineralization and stratigraphy.
Bunker Hill is therefore now employing 3D geologic modeling to expand on these geologic concepts, enabling reconstruction of the original position of the vein structures prior to post-mineral segmentation by faulting. This will allow Bunker Hill to project offset portions of known veins with historic production and target previously unexplored vein intersections, as well as targeting specific zones of higher-grade silver/lead mineralization.
ABOUT THE MAIDEN RESOURCE
The resource estimate was undertaken by Resource Development Associates (“RDA”) of Denver, Colo., and is based on RDA’s independently recommended program which verified the 1991 Bunker Hill historic reserves. Verification included the collection of 753 drift rib and back channel samples, totaling 3,765 feet, taken from existing accessible open mining stopes, as well as 43 diamond drill holes totaling approximately 9,200 feet of drilling.
Mineral resources are not mineral reserves and do not show demonstrated economic viability. All figures have been rounded to reflect the relative accuracy of the estimates. Underground mineral resources are reported at a cut-off grade of 3.3% ZnEq grade assuming: metal price of $1.10 per pound of Zinc, mining cost of US$50 per tonne, G&A cost of $6 per tonne, processing cost of US$10 tonne, and process recovery of 96 percent.
The grade estimation in this 43-101 resource was arrived at by verifying the estimation process and comparing the results to the estimation of the historic reserves. All mineralized block calculations were reviewed and verified by RDA resulting several mineralized blocks being excluded because historic estimate calculations could not be found and verified.
Estimations were conducted by condensing and translating drifts and stopes to vertical in sections on which mineralized envelopes were drafted. The polygonal end area of the mineralization was determined by the use of a planimeter and the average grade of samples ware used for the grade estimate. Grade estimates were updated quarterly, bi-annually and annually depending upon the reporting requirements of the mine as well as when reconciliation dictated.
The history of the estimation of mineral resources at Bunker is well-documented through the decades until mine closed. Tens of thousands of assays were gathered through the decades by well-established sample collection methods. Ore cars were sampled on a continual basis throughout the mine every five feet. Samples were assayed and results compiled by the mine’s technical staff of engineers and geologists. Grade estimation procedures were based on industry best practices at the time of estimation.
As a perennial mining operation throughout the 1900’s Bunker Hill reported reserves in accordance with widely accepted norms. Mining ceased at Bunker Hill in 1991, well before the adoption of NI 43-101. Despite the mine being in care and maintenance since 1991 the project still hosts estimated mineral quantities that demonstrate reasonable prospects for eventual economic extraction. Industry best practices suggest that resource classification should consider the quantity and quality of exploration data supporting the estimates, the confidence in the geological continuity of the mineralized zones, the geostatistical confidence in the tonnage and grade estimates, and the continuity at the reporting cut-off grade. As Bunker continues to modernize and digitize the voluminous historic data set, tests and verifies mineralization through sampling and drilling programs, invests in further exploration, and continues to conduct care and maintenance activities at the mine, it is clear that at this time a 43-101 compliant resource based on historic reserves can be classified in accordance with CIM definition standards. RDA recommends that the historic reserves at Bunker Hill be classified as Inferred Mineral Resources and will file a NI 43-101 technical report within the required timeframe.
