Submarine volcanism

Geology of the province is composed of Paleozoic basements. Tertiary altered submarine volcanic and sedimentary rocks (Green tuff) and Quaternary volcanic rocks. The basements are shale, tuff, limestone and chert of unknown ages. A simplified geologic map is shown in Fig. 1.148. 

The vein-type deposits can be divided into two based on the metals produced precious (Au, Ag) and base metal (Pb, Zn, Ag, Mn, Cu, Fe) vein-types. There are two sub-types of the base metal vein-type deposits, the Cu-Pb-Zn sub-type and the Pb- Zn-Mn-Ag sub-type. Cu-Pb-Zn veins occur in southern part of the province. Large Pb-Zn-Mn-Ag veins and Au-Ag veins are distributed in northeastern part. In the northeastern part, Au-Ag vein-type deposits occur in marginal zones of the province, while the base metal-rich deposits (Pb-Zn-Mn veins and Kuroko deposits) in central zone (Fig. 1.149). The marginal zone is characterized by exposure of Quaternary volcanic rocks and Plio-Pleistocene volcanic rocks in which Au-Ag veins occur, whereas the central zone is by thick submarine volcanic rocks (Fig. 1.150), in which base metal-rich deposits (base metal veins and Kuroko deposits) occur (Fig. 1.150). Tertiary volcanic rocks, Quaternary volcanic rocks and faults are distributed, trending generally from NW to SE. Some Cu-Pb-Zn veins in southern part are hosted by basement rocks. On the other hand, Pb-Zn-Mn-Ag and Au-Ag veins occur in Tertiary and Quaternary volcanic rocks. 

It is inferred that in the northern part of the province submarine volcanic rocks are thick in the central zone, while at marginal zone it is thin and the Plio-Pleistocene subaerial volcanic rocks are exposed. The vein-type deposits occur widely in the province. The precious vein-type deposits occur in relatively young (Plio-Pleistocene) volcanic rocks, while large base metal vein-type deposits (e.g., Toyoha, Inakuraishi, Ohe) and Kuroko deposits (e.g., Kunitomi) occur in central zone where thick Miocene submarine volcanic rocks are distributed (Figs. 1.149 and 1.150). Small base metal vein-type deposits occur in Paleozoic rocks in the southern part. 

During Miocene age most of this province was in a submarine environment. Violent submarine volcanism (bimodal and basic type) took place at Miocene age in this province. This geologic environment may be related to an extensional stress regime (Uyeda and Kanamori, 1979). The Kuroko deposits have been formed related to this tectonic situation. 

This submarine vs. subaerial hypothesis for the origin of the two types of deposits (Kuroko deposits, epithermal vein-type deposits) can reasonably explain the difference in metals enriched into the deposits by HSAB (hard-soft acids and bases) principle proposed by Pearson (1963) (Shikazono and Shimizu, 1992). Relatively hard elements (base metal elements such as Cu, Pb, Zn, Mn, Fe) are extracted by chloride-rich fluids of seawater origin, while soft elements (Au, Ag, Hg, Tl, etc.) are not. Hard elements tend to form chloro complexes in the chloride-rich fluid, while soft elements form the complexes in H2S-rich and chloride-poor fluids. Cl in ore fluids is thought to have been derived from seawater trapped in the submarine volcanic and sedimentary rocks. 

Most are in association with the products of basic submarine volcanic activities or their metamorphosed equivalents. 

As mentioned already in Chapter 2, submarine volcanism occurs not only at midoceanic ridges but also at subduction-related tectonic settings such as the Shikoku and Daito Basins, Farce Vela Basins, and Mariana Trough, Okinawa Trough and Izu Bonin Arc (e.g.. Wood et al., 1980 Dick, 1982 Delaney and Boyle, 1986). 

The total volume of volcanic rocks that erupted at back-arc basins in the circum-Pacific region during the early to middle Miocene is difficult to estimate. However, it is likely that the total volume of submarine volcanic rocks that erupted during early to... 

Previous studies demonstrated that the CO2 fluxes by hydrothermal solution and volcanic gas from midoceanic ridges play an important role in the global CO2 cycle and affect the CO2 concentration in the atmosphere (e.g., Javoy, 1988). However, submarine volcanism and hydrothermal activity occur not only at midoceanic ridges but also at island arc and back-arc basins as already noted. 

The ore fluids responsible for epithermal base-metal vein-type deposits were generated predominantly by meteoric water-rock interaction at elevated temperatures (200-350°C). Fossil seawater in marine sediments was also involved in the ore fluids responsible for this type of deposits. Epithermal precious metal ore fluids were generated by meteoric water-rock interaction at 150-250°C. Small amounts of seawater sulfate were involved in the ore fluids responsible for epithermal precious metal vein-type deposits occurring in Green tuff region (submarine volcanic and sedimentary rocks). 

Volcano-sedimentary ore deposits are syngenetic deposits precipitated from sea water enriched in metals by submarine volcanic activity. Deposits of this type are also called submarine exhalative-sedimentary deposits. Stratabound lead-zinc-copper deposits associated with marine sedimentary volcanic sequences belong to this category. Important examples are Kuroko deposit in Japan, Mt. Isa in Australia, Sullivan deposit in British Columbia, Canada, Rammelsberg in Germany and Rampura-Agucha in Rajasthan, India. 

Reed, M. H., 1977, Calculations of hydrothermal metasomatism and ore deposition in submarine volcanic rocks with special reference to the West Shasta district, California. Ph.D. dissertation, University of California, Berkeley. 

Large, R.R., McPhie, J., Gemmell, J.B., Herrmann, W., Davidson, G.J. 2001b. The speotrum of ore deposit types, volcanic environments, alteration halos and related exploration vectors in submarine volcanic successions some examples from Australia. Economic Geology, 96, 913-938. 

To the category of ancient hydrothermal seafloor ore deposits belong volcanic associated massive sulfide deposits. They are characterized by massive Cu-Pb-Zn-Fe sulfide ores associated with submarine volcanic rocks. They appear to have been formed near the seafloor by submarine hot springs at temperatures of 150-350°C. Massive sulfide deposits have 5 S-values typically between zero and the 5-value of contemporaneous oceanic sulfate, whereas the sulfate has 5-values similar to or higher than contemporaneous sea water. According to Ohmoto et al. (1983) the ore-forming fluid is evolved sea water fixed as disseminated anhydrite and then reduced by ferrous iron and organic carbon in the rocks. 

Hematitic iron ores of hydrothermal-sedimentary origin and Palaeozoic in age, are those of the Lahn-Dill-type in West and Central Europe (Harder, 1964). Hydro-thermal solutions associated with submarine volcanic activities have transported Fe (as FeCl3) into a marine environment, where after hydrolysis, hematite was formed (via ferrihydrite) at the margin of the basin, whereas siderite (after reduction) was formed in its centre. These ores are - in contrast to true sedimentary ores - low in Al,Ti and trace elements, which betrays their volcanic origin. 

Fig. 9.10. TAS diagram for submarine volcanism from the Tyrrhenian Sea. Compositions have been recalculated on a water-free basis.

Beccaluva L, Colantoni P, Di Girolamo P, Savelli C (1981) Upper-Miocene submarine volcanism in the Strait of Sicily (Banco Senza Nome). Bull Volcanol 44 573-581... 

To obtain information on the noble gas state in the mantle, it is necessary to analyze mantle-derived materials that have trapped mantle noble gases. Accessible samples include volcanic rocks, volcanic gases, mantle xenoliths, and diamonds. Among various mantle-derived materials, submarine volcanic rocks are particularly useful because of their wide occurrence and their relatively large (for mantle samples) amounts of trapped noble gases. So far, information has been obtained mainly from... 

Most submarine volcanic rocks contain C02-filled vesicles (bubbles) in glassy margins. Because noble gases in silicate melts partition very effectively into a gas phase (i.e., their solubilities are low), it would be expected that noble gases in submarine volcanics would be found in the bubbles as will be discussed later, this seems indeed to be the case (e.g., Kurz Jenkins, 1981 Marty Ozima, 1986 Sarda Graham, 1990 Graham Sarda, 1991). The popping rocks, so-called because of... 

The cherty iron-metabasite formation (CIM) was formed in regions of submarine volcanism of basic composition. The iron cherts in the formation are not uniform in facies and amount to 10-30% of the total thickness of the sequence. The formation is extensively developed in the lower metabasic series of the Konka, Belozerka, Verkhovtsevo, and Sura synclines. 

The significance of Shatskiy s scheme is the fact that it presumes heterogeneity of the cherty jaspilitic formation, which can arise both from products of submarine volcanism and as a result of transport of materials from the weathering of volcanic rocks on land. It is assumed that the remote jaspilitic... 

Semenenko et al. (1959, 1967) assigned a large role in the formation of the iron cherts of the Ukrainian shield to processes of volcanism. According to his formational scheme, a direct relationship to submarine volcanism is established for the CIM, CIU, and CIK, from the paragenetic association of iron cherts with volcanic rocks. 

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