Tungsten ore veins cutting granite at Cligga Head

The reaction of tin/tungsten chloride-bearing fluids with granite produces economically important greisen veins. The mine at Cligga head in the St Agnes region of Cornwall was the main source of Britain's tungsten during the first part of the 20th century and the sub-economic veins left over provide a perfect example to see how the late-stage hydrous fluids from the intrusion interacted with the cooling granite to produce the important ore minerals cassiterite and wolframite.

[@lineinthesand663]

Lovely video thank-you. Instructive. Work in exploration in Namibia and have done quite a little Sn work.

[@OneMinuteGeology]

Thank you. Glad you like it.

[@lineinthesand663]

@@OneMinuteGeology Are there examples of greisen-type mineralisation at higher levels? ie: Purely hydrothermal systems hosted in other lithologies? We have a smallish province of solely quartz vein hosted Sn/W set in the NeoProterozoic turbidites from which the S-Type granites arose.

[@OneMinuteGeology]

@@lineinthesand663 no, the greisen reaction is specifically an acid dissolution of orthoclase feldspar to make muscovite and quartz plos potassium chloride in solution.. So it is pretty much limited to within granites. The metals come out as the pH of the fluid increases during the reaction. ThERe ARE otherways to destabilise the oxy-chloride complexes which transport tin and tungsten, including increasing pH, oxidising the solution or changing P-T conditions. Those can all happen outside a source magma body.

[@canadiangemstones7636]

Excellent video, thanks!

[@OneMinuteGeology]

Glad you like it.

[@chancebutler6472]

tyvm

[@pertechnetyl]

SnF4, not SnCl4.

[@OneMinuteGeology]

Mainly chlorine. See the 2021 review by Lehman in Lithos, for example