South Crofty Tin Project, UK

The South Crofty Tin Project is a historical underground tin mine located in the Cornwall central mining district in southwest England.

Canadian mineral exploration company Cornish Metals (previously Strongbow Exploration) is working to reopen the tin mine.

The current South Crofty project consists of two former producing mines- South Crofty and Dolcoath.

Cornish has received all the necessary permits to dewater the mine. The company is advancing studies to reach a production decision.

In April 2024, the company announced positive Preliminary Economic Assessment (PEA) for the South Crofty Tin Project.

According to the report, the mine can produce 49,310 tonnes of tin metal in concentrate over a 14-year life of mine (LOM).

It will employ up to 320 people directly and create up to 1,000 indirect jobs.

The PEA also confirmed the economic viability of the project with a base case after-tax Net Present Value (NPV) of $201m. Pre-production capital requirement is estimated to be $177m.

It is a fully permitted project with mining permission through to 2071. A full planning permission is also in place to build a processing plant to recover tin concentrate.

In November 2024, Cornish developed a near mine exploration target that has the potentiality to expand the current mineral resource at South Crofty.

The Water Treatment Plant to dewater the mine was commissioned in October 2023, with the removal expected to be completed in the third quarter of 2025.

South Crofty Project Location

South Crofty is located in the parish of Pool between the towns of Redruth and Camborne, in the Central tin mining district of Cornwall, the UK.

The mine is approximately 4.5km south of the northeast coast of Cornwall and the Celtic Sea and approximately 390km from London.

It covers an area of 1,490 hectares (ha) with 1,500m working depth below surface. The area extends over 26 historic mining operations.

The tin project is accessible via the main A30 trunk road from London to Land’s End in Cornwall. The road is situated 1km south of the project.

South Crofty Project History

Tin mining in this area can be traced back to 2,300BCE with large-scale production at South Crofty dating back to mid-1600s.

It produced intermittently until its final closure in 1998 when low tin prices led to suspension in production.

South Crofty produced 191,200 tonnes on an average from 1984 to 1998 at an average grade of 1.31% Sn.

Ownership history dates back to 1906 after South Crofty (SCL) was established to mine the tin deposits located beneath historic copper mines in the area. Since then, the project went through multiple changes in ownership.

In 2016, Cornish Metals acquired a 100% interest in Western United Mines (WUML) and Cornish Minerals (Bermuda), the owners of the property. The acquisition included additional 7,500 hectares located in various parts of Cornwall.

Geology and Mineralisation

South Crofty is located on the northern part of the Permian Carn Brea Granite that may be connected with the Cornubian batholith at depth. The geology is characterised by granitic intrusions belonging to Permian Cornubian batholith, while Devonian metasedimentary and metavolcanics form the metamorphic aureole and host rocks of the intrusions.

The Great Crosscourse, a late fault, bisects the project and divides it into two areas- east and west.

The mine area is underlain by metasedimentary and metavolcanic rocks (killas) along with skarns and hornfels present in contact with granite which covers the complete project area.

The mineralisation of the mine is found in vein-type structures (lodes) striking east-north-east and parallel to the granite/killas contact.

The tin deposit is classified as an intrusion-related, structurally controlled and vein-hosted mineralisation.

In granite, the main mineral present is cassiterite. Zinc and copper sulphide mineralisation is also present above the granite contact.

South Crofty Project Mineral Resource Estimate

The mineral resource estimate is divided into two areas.

The Upper Mine mineral resource is predominantly polymetallic tin-copper-zinc mineralisation hosted within a metasedimentary country rock, while the Lower Mine resource consists of tin hosted predominantly within granite.

At 0.6% tin equivalent (SnEq) cut-off, the indicated mineral resource estimate for the upper mine is 260 kilo tonnes (kt) containing 2,583t of tin equivalent (SnEq) at a grading of 0.99% and tin (Sn), copper (Cu), and zinc (Zn) at gradings of 0.69%, 0.78%, and 0.59%.

The inferred mineral resource estimate for the upper mine is 465kt containing tin, copper, and zinc at gradings of 0.66%, 0.63%, and 0.63% respectively with 4,239t SnEq at a grading of 0.91%.

At same SnEq cut-off, the indicated mineral resource estimate for the lower mine is 2,896kt containing 43,573t tin at a grading of 1.50%.

The inferred mineral resource for the lower mine stands at 2,626kt containing 37,364t tin at a grading of 1.42%.

Mining and Processing

The South Crofty underground project will be mined using Sub-Level Open Stoping (SLOS) methods.

A sub-level between main levels will be used with upholes and downholes to reduce drill length. For backfilling the existing mining spaces, it would use paste backfill.

The production rate from the mine is planned at 1,400 tonnes per day (t/d) with a total of 6Mt of mineralised material expected to be extracted over the operating life.

The existing NCK main shaft and main levels, spaced approximately every 45m, will be used for underground operations.

Ramps are planned for new developments providing the mobile fleet with access throughout the mine.

The material from the lower mine will be hoisted by the NCK shaft and the material from the upper mine will be trucked with the support from extensions.

The ROM will be fed into a primary single stage crushing circuit. The crushed material will undergo secondary crushing followed by X-Ray Transmission (XRT) ore sorting and Dense Media Separation (DMS).

The separated XRT material will be screened again with +15 mm material reporting to a vibrating feeder and closed circuit 132kW tertiary cone crusher. The -15 mm+0.85 mm material will pass to the 430t rod mill feed storage bin and -0.85 mm will be transferred to the Fines Screening Area.

The grinded material may undergo polymetallic flotation.

Ball mill product and crusher fines (d80 = 150 µm) will be pumped via hydrocyclones to buffer tanks. The classified feed is deslimed and directed into a multispigot hydrosizer (MSH) for separation, followed by treatment on shaking tables and multi-gravity separators (MGS).

Tailings from the primary gravity circuit will be re-grounded in a ball mill operating with hydrocyclones, deslimed, and fractionated by a secondary MSH before further processing on shaking tables and MGS.

Slimes from the gravity circuits are treated using Falcon concentrators, with the concentrate cleaned via MGS and tailings directed to the thickener. The bulk concentrates (Sn + S = 52-54%) from spiral and gravity processes undergo sulphide flotation to remove impurities, reducing smelter penalties.

The tin dressing concentrate will be then combined with tertiary MGS output, filtered, and packaged.

Tailings for the process will be thickened to 60-65% solids for use as underground cemented backfill.

The processing plant is expected to have a production rate of 500,000 tpa initially, which will be ramped up to 800,000 tpa. The tin concentrate produced at the facility will undergo smelting at off-site locations.

South Crofty Project Infrastructure

The main infrastructure of the mine includes a concentrator plant, an assay laboratory, a Mine Water Treatment Plant (MWTP), a backfill plant, a temporary tailings storage facility, onsite access roads etc.

The mine will receive power from the National Grid electricity with two 33kV and one 11kV lines crossing the site. The grid power is also available at 132kV within 1km of the mine area.

Power supply at the site is expected to be upgraded to support new operations.

For emergencies, a back-up generator is installed. It is a diesel-powered 550kVA/415V generator feeding the mine.

Key Contractors Involved

AMC Consultants, a mining consultancy and engineering firm, prepared the 2024 PEA, 2023 and 2021 technical reports for the South Crofty Tin Project.

In October 2024, Endeavour Financial was selected as the financial advisor for the tin project.

Resource Estimates and two technical reports for the mine in 2011 and 2012 were prepared by Micromine.

In October 2018, Cornish, via its subsidiary WUML, and OMF Fund II H, an affiliate of Orion Mine Finance, entered into an offtake agreement related to the project.

Canadian mineral industry consultancy firm P&E Mining Consultants was engaged to prepare the mineral resource estimate for the Upper Mine in April 2016.

Siltbuster Process Solutions, a packaged plant environmental solutions provider in the UK, and Nomenca, a UK construction engineering company, were selected in June 2017 for process specification and outline design works for the water treatment plant of the project.