Tamarugite forms inside a grotto excavated in hydrothermally altered andesitic rocks at the gold mine of Furtei, Sardinia, Italy. The mineral mainly occurs as single phase in globular aggregates, with only small amounts of gypsum, halite and halotrichite-pickeringite. Tamarugite also occurs intimately mixed with alunogen and pickeringite-halotrichite, or associated with alunogen and magnesian aubertite. The formation of tamarugite is the result of the interaction between acidic sulfate waters, deriving from oxidation of disseminated sulfides (mainly pyrite), and the hydrothermally altered country rocks. The arid conditions of the Furtei area favour the formation of tamarugite and other water-soluble secondary minerals of evaporation of the scanty, saline waters percolating through the walls of the grotto. Unlike other world tamarugite occurrences, the main source of sodium is not sea spray, but can be referred to the sodium content of the volcanic rocks which were affected by hydrothermal circulation. A least-squares unit-cell refinement of 47 reflections from X-ray powder diffraction analysis of the Furtei tamarugite gave the following results for a monoclinic cell: a = 7.358(2), Å, b = 25.244(9) Å, c = 6.095(2) Å, β = 95.16(4)°, V = 1127.4(5) Å3.
Tamarugite from the gold mine of Furtei, Sardinia, Italy
FRAU, FRANCO;DA PELO, STEFANIA
1999-01-01
Abstract
Tamarugite forms inside a grotto excavated in hydrothermally altered andesitic rocks at the gold mine of Furtei, Sardinia, Italy. The mineral mainly occurs as single phase in globular aggregates, with only small amounts of gypsum, halite and halotrichite-pickeringite. Tamarugite also occurs intimately mixed with alunogen and pickeringite-halotrichite, or associated with alunogen and magnesian aubertite. The formation of tamarugite is the result of the interaction between acidic sulfate waters, deriving from oxidation of disseminated sulfides (mainly pyrite), and the hydrothermally altered country rocks. The arid conditions of the Furtei area favour the formation of tamarugite and other water-soluble secondary minerals of evaporation of the scanty, saline waters percolating through the walls of the grotto. Unlike other world tamarugite occurrences, the main source of sodium is not sea spray, but can be referred to the sodium content of the volcanic rocks which were affected by hydrothermal circulation. A least-squares unit-cell refinement of 47 reflections from X-ray powder diffraction analysis of the Furtei tamarugite gave the following results for a monoclinic cell: a = 7.358(2), Å, b = 25.244(9) Å, c = 6.095(2) Å, β = 95.16(4)°, V = 1127.4(5) Å3.
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