The Cae Coch volcanogenic massive sulphide deposit, Trefriw, North Wales

The Cae Coch massive pyrite deposit is described and re-interpreted as a sedimentary volcanogenic orebody of about 200 000 tons. It is located at the contact between the Ordovician Dolgarrog Volcanic Formation (basic tuffs and lavas) and the overlying Llanrychwyn Slates (pyritic black mudstone) and close to a major intrusive rhyolite. The minerals are dominantly pyrite and quartz with minor molybdenite and the deposit shows zonal variation in trace Ba, Cu, Zn, Ni, and Co and detectable concentrations of Sn, TI, Hg and Ag. The footwall rocks have been highly altered and the basic rocks show increases in K, Ba, S and carbonate and losses of Cu, V and Co and probably light rare earth elements (LREE). A progressive gain in K, Ba and Pb and a depletion of Ga, Sr, Sn, Zn and REE is observed with increasing alteration of the rhyolite. The deposit is concluded to be the result of accumulation in a brine pool but with a component of debris flow of uncertain provenance. The deposit resembles Kuroko style mineralization and seems to be unique in the immediate district.

[1]  S. Campbell,et al.  Volcanogenic mineralization related to the Snowdon Volcanic Group (Ordovician), Gwynedd, North Wales , 1985, Journal of the Geological Society.

[2]  D. Banks.  A fossil hydrothermal worm assemblage from the Tynagh lead–zinc deposit in Ireland , 1985, Nature.

[3]  P. Thurston,et al.  Rare-earth element mobility in alteration pipes below massive CuZn-sulfide deposits , 1984 .

[4]  M. J. Russell,et al.  Formation of fossil hydrothermal chimneys and mounds from Silvermines, Ireland , 1983, Nature.

[5]  A. Boyce,et al.  Hydrothermal pyrite chimneys from the Ballynoe baryte deposit, Silvermines, County Tipperary, Ireland , 1981 .

[6]  B. Roberts.  Low grade and very low grade regional metabasic Ordovician rocks of Llŷn and Snowdonia, Gwynedd, North Wales , 1981, Geological Magazine.

[7]  G. Sabatini,et al.  A revaluation of the Co/Ni ratio in pyrite as geochemical tool in ore genesis problems , 1979 .

[8]  Robert G. Garnett.  Applications of Probability Graphs in Mineral Exploration , 1977 .

[9]  Julian A. Pearce,et al.  Tectonic setting of basic volcanic rocks determined using trace element analyses , 1973 .

[10]  J. D. Vine,et al.  Geochemistry of black shale deposits; a summary report , 1970 .

[11]  M. Solomon,et al.  Cobalt, nickel and selenium in sulphides as indicators of ore genesis , 1967 .

[12]  R. L. Sherlock.  The Geology and Genesis of the Trefriw Perites Deposit , 1918, Quarterly Journal of the Geological Society of London.

[13]  J. Lydon.  Some observations on the mineralogical and chemical zonation patterns of volcanogenic sulphide deposits of Cyprus , 1984 .

[14]  B. P. Kokelaar,et al.  The Ordovician marginal basin of Wales , 1984, Geological Society, London, Special Publications.

[15]  B. Skinner,et al.  The Kuroko and Related Volcanogenic Massive Sulfide Deposits Introduction and Summary of New Findings , 1983 .

[16]  J. Date,et al.  Zonal Alteration around the Fukazawa Kuroko Deposits, Akita Prefecture, Northern Japan , 1983 .

[17]  S. Scott,et al.  A Comparison of Footwall-Rock Alteration and Geothermal Systems Beneath Some Japanese and Canadian Volcanogenic Massive Sulfide Deposits , 1983 .

[18]  Hironori Hashiguchi,et al.  Practical Application of Low Na 2 O Anomalies in Footwall Acid Lava for Delimiting Promising Areas around the Kosaka and Fukazawa Kuroko Deposits, Akita Prefecture, Japan , 1983 .

[19]  S. Scott,et al.  Mineralogy, Geochemistry, and Mineral Chemistry of Siliceous Ore and Altered Footwall Rocks in the Uwamuki 2 and 4 Deposits, Kosaka Mine, Hokuroku District, Japan , 1983 .

[20]  J. Platt.  Volcanogenic mineralization at Avoca, Co. Wicklow, Ireland, and its regional implications , 1977, Geological Society, London, Special Publications.

[21]  J. Winchester,et al.  Geochemical discrimination of different magma series and their differentiation products using immobile elements , 1977 .