Largest Sulfide Deposits Research Articles

An intermittent detachment faulting system with a large sulfide deposit revealed by multi-scale magnetic surveys

Magmatic and tectonic processes can contribute to discontinuous crustal accretion and play an important role in hydrothermal circulation at ultraslow-spreading ridges, however, it is difficult to accurately describe the processes without an age framework to constrain crustal evolution. Here we report on a multi-scale magnetic survey that provides constraints on the fine-scale evolution of a detachment faulting system that hosts hydrothermal activity at 49.7°E on the Southwest Indian Ridge. Reconstruction of the multi-stage detachment faulting history shows a previous episode of detachment faulting took place 0.76~1.48 My BP, while the present fault has been active for the past ~0.33 My and is just in the prime of life. This fault sustains hydrothermal circulation that has the potential for developing a large sulfide deposit. High resolution multiscale magnetics allows us to constrain the relative balance between periods of detachment faulting and magmatism to better describe accretionary processes on an ultraslow spreading ridge.

Pyrrhotite mineralization as a search criterion for sulfide deposits at sediment-covered spreading centers

Pyrrhotite ores forming the hydrothermal vents of the Hydrothermal Hills in the Southern Trough of the Guaymas depression were studied. A series of features pointing to the occurrence of surface and buried sulfide deposits of pyrrhotite mineralization was revealed: the presence of pyrrhotite associations to hydrocarbons of oil series; low concentrations of Cu, Zn, and Pb; the enrichment of sulfur of pyrrhotite and hydrogen sulfide of hydrothermal solutions in heavy 34S isotope by 5–7%; and the heavy isotope composition of carbon in naphthoid compounds. The results obtained allow one to suggest searching for large sulfide deposits at active rifts of high spreading and sedimentation rates, i.e., at near-continental rifts of the humid zone of avalanche sedimentation.

Copper Isotope Systematics of the Lucky Strike, Rainbow, and Logatchev Sea-Floor Hydrothermal Fields on the Mid-Atlantic Ridge

In this paper, we present the copper isotope signatures of black smoker sulfides, massive sulfides, and their alteration products and provide new insights into mineralization processes and applications of copper isotope geochemistry to sea-floor hydrothermal systems on the Mid-Atlantic Ridge. The hydrothermal systems studied include the Lucky Strike field at 37°17'N on a basaltic substrate and the Rainbow and Logatchev fields, situated on ultramafic rock. Copper isotope variation in the hydrothermal precipitates was examined in conjunction with S isotopes and Se and Co concentrations. The comparison between δ 65Cu and Se contents shows that subsurface precipitation of Cu-rich sulfides does not control significantly the δ 65Cu values of the hydrothermal chimneys. It appears that the major cause of copper isotope fractionation in hydrothermal systems (up to 3‰) is the sea-floor oxidation of primary copper sulfides. Enrichment in the heavy copper isotope can be explained by processes occurring at the sea floor, such as hydrothermal reworking of previously altered sulfides by high-temperature fluid. Massive sulfides characterized by negative δ 65Cu values have undergone extensive recrystallization. In these mineralogical assemblages, isotopically heavy copper typical of altered sulfides has been leached and redeposited in the external zones or incorporated in hydrothermal fluids. Copper isotopes are therefore a promising tool for the study of supergene processes and the recycling of previously oxidized sulfides, as well as a means of characterizing the degree of hydrothermal reworking of large sulfide deposits. Further studies of copper isotope fractionation under controlled laboratory experimental conditions are required to identify copper isotope fractionation during sulfide alteration. In particular, the possible biological mediation of copper isotope fractionation during sulfide oxidation may be an important direction for further studies.

Mercury in the Tinto-Odiel Estuarine System (Gulf of Cádiz, Spain): Sources and Dispersion

The Tinto and Odiel are small rivers draining one of the largest sulphide deposits in the world. As a result of these deposits and a large industrial complex, the adjacent marine area receives a high amount of metal input. Mercury distribution in the Tinto-Odiel estuary, the Huelva Ria and the Gulf of Cadiz was assessed in water and suspended particulatematter (SPM) and sediments. In the rivers and estuaries, dissolved (HgD)and particulate (HgP) mercury showed wide variations (13 to 200 pM and0.3 to 330 nmol g-1 respectively) depending on the presence or notof sulphidic waters, phosphogypsum deposits, detrital pyrite and oxyhydroxides.In the Ria, concentrations were lower than 10 pM and 4.5 nmol g-1 for HgD and HgP respectively. In surface waters of the Gulf of Cadiz, the average HgD concentration (pm standard deviation) was 2.9 pm 0.9 pM, which is similar to that of North Atlantic Central Waters. The surface sediments collected in the rivers, the Ria and the Gulf showed systematically enriched mercury compared to pre-industrial levels. Vertical mercury profiles in dated sediment cores were typical of anthropogenically influenced environments starting in the early Roman age. These distribution features suggest that most of the Hg discharged by the Huelva Ria is trapped in the sediments of the Gulf of Cadiz.

Constraints on the energy and chemical balances of the modern TAG and ancient Cyprus seafloor sulfide deposits

The size, chemical composition, energy flux, and fluid composition of the TAG hydrothermal sulfide deposit at the Mid‐Atlantic Ridge and the size, chemical composition and reaction zone characteristics of the Skouriotissa volcanogenic massive sulfide deposit of the Troodos ophiolite in Cyprus are used to examine the energy requirements and chemical balances associated with the generation of a large volcanogenic massive sulfide deposit. We conclude that formation of large sulfide deposits from oceanic hydrothermal systems is a geologically rapid process and occurs on timescales of hundreds of years, with episodes of activity as short as a few tens of years separated by thousands of years of inactivity. About 2×1019 J of energy supplied at high temperature is required to form a deposit the size of the TAG mound. Metals (up to 4 times the mass of any element present in the sulfide deposit) are leached out of relatively small reaction zones most likely at the base of the sheeted dikes. Chemical balance can be struck for all elements except sulfur with a reaction zone 1–2 km3 in volume from which a small proportion of iron and large proportions of copper, zinc, and manganese are removed. A sulfur balance requires that a significant fraction of sulfur be derived from reduction of seawater sulfate, as suggested by stable isotope analyses. We argue that the principal source of energy that drives hydrothermal circulation is latent heat of crystallization of magma close to the top of the plutonic section. Furthermore, we speculate that activity of the TAG hydrothermal system is related to periods of more rapid magma supply from the mantle at magma supply rates similar to those observed in volcanoes in Hawaii and Iceland.

Where are the large hydrothermal sulphide deposits in the oceans?

Large sulphide deposits have been identified on slow and fast spreading ridges and backarc basins. Their formation is controlled by a combination of several conditions, each of which alone is often...

Mid-ocean ridge sulfide deposits: Evidence for heat extraction from magma chambers or cracking fronts?

Numerous seafloor observations show that the sizes of high-temperature hydrothermal sulfide edifices vary dramatically with spreading rate. On fast-spreading ridges venting occurs from spindly chimneys which reach heights of about 10 m, while on slow-spreading ridges vents are frequently located near the tops of large sulfide mounds whose volumes may reach 10 5–10 6 m 3. We argue that such variations are the result of a profound difference in the nature of hydrothermal heat extraction between fast-spreading ridges, where spreading occurs predominantly by magmatism, and slow-spreading ridges, where there is a significant component of tectonic extension. Along fast-spreading ridges, a steady-state axial magma chamber can be insulated by a relatively thick conductive boundary layer because heat extraction is limited by low permeability. In such systems, episodes of vigorous venting are linked to diking events not only because these introduce a significant heat source into the upper crust but also because the intrusion of a dike is the primary source of increased permeability near the ridge axis. Over a time scale of the order of a decade, mineral deposition tends to clog the reaction and upflow zones and there is a high probability that young sulfide structures will be buried by subsequent eruptions. On slow-spreading ridges, tectonic extension maintains the fluid pathways necessary to support vigorous convection. In the waning stages of magmatism, hydrothermal circulation driven by a downward-migrating cracking front can cool the entire crust leading to the formation of very large sulfide deposits. As the depth of circulation increases, overburden pressures reduce the permeability and the hydrothermal heat fluxes decrease progressively. Once hydrothermal fluids penetrate the Moho, serpentinization clogs the fluid pathways and high-temperature venting ceases until it is reactivated by a fresh magmatic intrusion.

Hydrothermal mineralization at seafloor spreading centers

Hydrothermal mineralization at seafloor spreading centers