Genesis of the Impregnation Sulphur Deposits
1956 Volume 6 Issue 19 Pages 1-12
Details
1956 Volume 6 Issue 19 Pages 1-12
Impregnation sulphur deposits and solfataric emanations of many volcanoes in Japan have been studied and based on that research the following hypothesis for the genesis of the impregnation sulphur deposits is proposed:
(1) The deposits tend to accumulate in geological structures such as alternating lava flows and pyroclastic rocks.
(2) Near the surface, iron sulphide and free sulphur are oxidized by oxygen in the atmosphere, thereby producing H2SO4 and Fe2(SO4)3.
(3) Meteoric water dissolves the H2SO4, Fe2(SO4)3, and atmospheric oxygen and flows into the ground and down through permeable rocks as tuff-breccia, agglomerate etc. to and along the upper surface of inclined impermeable stratum such as shaly tuff and lava flow etc.
(4) These rocks are heated by some heat source which exists in the depths of the volcano. The descending water reaching upon the rocks is soon heated and a part of it evaporated into steam.
(5) The mixed vapour of the steam and volcanic gas containing H2S, CO2, HCl etc. which is expelled from the magma, flows up vigorously in to the upper parts of the permeable rocks to and along the lower surface of an upper impermeable stratum, where the remains of the solution becomes mist and is carried away by the mixed vapour.
(6) H2SO4, Fe2(SO4)3 and oxygen dissolved in the mist react to H2S to form free sulphur as follows,
3H2S+H2SO4=4H2O+4S
2H2S+O2=2H2O+2S
4H2S+Fe2(SO4)3=2FeSO4+4H2O+5S
(7) The mist is highly acid and it attacks the surrounding rocks and has them porous by dissolving the AL2O3, FeO, Fe2O3, MgO, CaO, K2O, . Na2O etc.
(8) The free sulphur fills up the interspaces and the silica of the original rock minerals remains in place as opal. In this manner the sulphur rich ore is made.
(9) The temperature at the time of sulphur deposition is presumed to be from about 120°to 150°C, and the pressure about 2 to 4 atm..
(10) Under the upper impermeable stratum, the acidity of the mist is less than that of the mist near the lower impermeable one. Most iron sulphide ore is made near the upper stratum because the enviroment at that place is more suitable for the precipitation of iron sulphide.
(11) In the rocks adjacent to the deposit and near the upper surface of the under impermeable stratum, the temperature is lower than that of the middle part of the deposit and opalization is predominant.
(12) The solfataric gas, containing steam, H2S, FeSO4, some free sulphur, and mist of hydrothermal solution ascends to the surface and issues from the solfatara.
(13) The atomospheric oxygen oxidizes the solfataric gas again and the cycle is repeated.
