Mining company Cornish Metals Inc has discovered more copper, tin, zinc and silver at its United Downs project in the duchy.
The Canadian-headquartered company has released the results from two drillings and said it found the metals including some “exceptionally high” tin grades.
The company, formerly known as Strongbow, added a second drilling rig at United Downs (UD) in September 2021 after raising £8.2m for the project by selling shares on the Stock Exchange’s AIM.
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Richard Williams, chief executive of Cornish Metals, said: “These results continue to demonstrate the presence of multiple mineralised structures within the UD Lode target area.
“The intercepts in the latest holes do not appear to be part of UD Lode itself but represent new sub-parallel zones of mineralisation, including some exceptionally high tin grades.
“This is the first time we have encountered high-grade zinc mineralisation, which occurs as coarse black sphalerite, and also note the high silver grades associated with the copper-rich zones. Additional drilling is required to understand the geometry and scale of these zones.”
He added: “The continued discovery of new mineralization by the current drilling underscores the prospective and under-explored nature of the United Downs area for near surface tin, copper, zinc and silver. The drill programme continues and results will be reported as and when received.”
The geology at United Downs comprises metasediments - locally termed “killas” - which overlie an intrusive granite body. All the historic copper mines within the area - United Mines and Consolidated Mines - and the historic tin, copper and zinc mines - Mount Wellington and Wheal Jane - mined entirely within killas.
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The mineralisation is primarily in narrow, steeply dipping vein or “lode” structures, and consists of cassiterite (tin), chalcopyrite (copper) and sphalerite (zinc) with other copper minerals such as chalcocite and bornite occasionally present.
United Mines and Consolidated Mines, located 200m south and 400m north of UD Lode, respectively, operated between the early 1700s and the 1870s, mining high-grade copper ores, with reported grades of 7.5% copper, to depths of up to 500m below surface.
Mount Wellington and Wheal Jane mines exploited similar structures located along strike from the historic mining at United Downs, where tin, copper and zinc was mined and processed until 1978 and 1991, respectively.
Wheal Jane was mined to a depth of about 500m below surface whereas Mount Wellington only reached about 200m depth before closing. Mount Wellington is located within Cornish Metals’ mineral rights and was still in mineralisation when the mine closed.
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Drilling at United Downs is being performed by Priority Drilling Company Ltd using an Epiroc Christensen CT14 Diamond Drill Rig. Mineralised zones were drilled in NQ (76mm) diameter) to recover a 48mm diameter drill core. Core recovery was greater than 95%. The core was logged, split and sampled by Cornish Metals personnel.
The samples, comprising half core, were sent for assay at ALS Minerals, Loughrea, Ireland. Sample preparation involved crushing to 70% less than 2mm, riffle split and pulverised to 85% less than 75 microns. The analytical method used was X-ray fluorescence (XRF) following a lithium borate fusion.