Brownfield Exploration Reconnaissance and Assessment of the Botallack Mine Site

Summary

The Botala mine in southwest Cornwall, historically a significant source of tin and copper, has been the subject of recent geological mapping. The study investigates the mineralization styles, tectonic history, and potential for brownfield exploration in the region. The site contains valuable minerals like tin, copper, and uranium, but challenges such as hazardous materials, environmental impacts, and strict legal protections complicate the viability of reopening the mine. The project could contribute to the green energy transition and local job creation, but it faces opposition due to its proximity to protected areas and tourist sites.

Takeaways

• 😀 Botala was a major mining district in southwest Cornwall during the 18th century, producing significant amounts of tin and copper.
• 🌍 Geological mapping of the area aimed to assess its potential as a brownfield exploration target, with a focus on mineralization styles and geometry.
• 🗺️ The region experienced several tectonic episodes, including passive margin development and post-convergence extension in the Permian period.
• ⚒️ Various mineralization types were identified, including polymetallic veins, tin floors, and copper mineralization linked to granite magmatic fluids.
• 🔎 Significant mineralization features include disseminated sulfides, tourmaline veins, and the presence of secondary copper and uranium minerals.
• 📊 The estimated exploitable tin in the area is 800 tons at a grade of 1.8%, valued at around 27 million USD at current prices.
• ⛏️ The mine has had three separate working periods, with the most significant mining occurring from 1721 to 1895, then brief revivals in the early 1900s and 1980s.
• 🔬 Historical ore processing methods involved crushing, shaking tables, and arsenic calcining, highlighting the complex handling of toxic materials.
• ⚠️ Environmental concerns include the potential release of hazardous materials like arsenic and uranium, complicating remediation and mining operations.
• 📈 The economic viability of reopening the mine depends on factors such as fluctuating metal prices, local opposition, and strict environmental protections due to its heritage status.

Q & A

What was the historical significance of Botala in Cornwall's mining industry?

Botala was a major contributor to Cornwall's mining industry during the 18th century, producing 15,000 tons of tin and 24,000 tons of copper. It played a pivotal role in the region's mining economy, particularly in the production of tin and copper ores.

What were the primary geological features that influenced the mineralization at Botala?

The primary geological features influencing mineralization at Botala include a combination of volcanic, sedimentary, and metamorphic rocks. Tectonic events such as the inversion of the passive margin, faulting, and granite intrusions were crucial in the formation of valuable minerals like tin, copper, arsenic, and uranium.

How were the mineralization styles at Botala classified?

The mineralization at Botala was classified into two main types: polymetallic veins or loads that strike northwest-southeast, and tin floors associated with granite. The latter are concentrated by magmatic fluids relating to the granite, while the former are cross-cut by granite structures.

What evidence was found regarding copper mineralization at Botala?

Copper mineralization at Botala was evidenced by the presence of copper minerals in quartz veins hosted in metapelites, as well as disseminated sulfides in the surrounding metamorphosed rocks. This copper is closely linked to the metamorphosed rocks overlying the granite.

How was the estimated tonnage of tin in the Botala site calculated?

The estimated tonnage of tin at Botala was calculated based on measurements of the tin floors, using the specific gravity of tourmaline and cassiterite. The total estimated tin tonnage in the ground is 48,355 tons, with a value of $27 million based on current tin prices.

What were the mining operations at Botala like, and when did they occur?

Mining at Botala began in 1721, with significant operations in the 18th and 19th centuries. The mine experienced three separate periods of mining activity: the first from 1721, the second in the early 1900s, and the third in the 1980s. Operations declined due to economic downturns, including a fall in tin prices and flooding incidents.

What were the main techniques used for processing ore at Botala during its second period of operation?

During the second period of operation, the ore at Botala was crushed using stamps, separated with shaking tables, and then further refined using bottles to separate out heavy minerals. The refined ore was roasted in an arsenic calciner to produce arsenic powder.

What economic factors affect the viability of reopening Botala mine?

The economic viability of reopening Botala depends on factors like the current high prices of tin and copper, potential job creation, and regional economic growth. However, uncertainty about the mine's profitability, the need for further exploration, and the condition of remaining ore deposits are critical challenges.

What environmental and social challenges might affect the reopening of Botala mine?

Environmental challenges include the presence of hazardous materials like arsenic and uranium, which pose contamination risks. Social challenges include the potential impact of increased traffic on local infrastructure, the generation of dust pollution, and the opposition from local residents and tourism stakeholders due to the site's protected status.

What mitigation strategies could address the environmental impacts of mining at Botala?

Mitigation strategies could include leaving the waste rock piles undisturbed to prevent further contamination, constructing alternative roads to reduce traffic impacts, and employing dust control measures such as spraying or wetting the dust piles. Additionally, focusing on primary ore extraction underground rather than processing waste rock could help minimize surface disturbances.