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By William J. Scott

In the last two years, C-CORE has developed a new seabed sampler directed specifically at obtaining samples from hard or compacted bottoms such as are typical of marine placer deposits. Samples are required for appraisal of concentrations of saleable commodities, and for determination of levels of biological indicators in the deposits. Recently C-CORE and the University of Victoria have been comparing the performance of the Scott/C-CORE sampler with that of the Van Veen sampler often used for biological sampling. Initial trials of the Scott/C-CORE sampler in 1992 at the WestGold mining site, Nome, Alaska, were described by Jewitt et al. at the 1993 UMI. Since that time the sampler has been modified to prevent overfilling, and to limit turbulent flow of water across the top of the sampler buckets when the sampler is recovered with partly-open buckets. The modifications included shoes to prevent sampler overfill, and flexible rubber shielding over top and sides of the sampler to prevent water circulation. Samples have been taken with both samplers in two field areas, one at Pine Cove, Baie Verte, Newfoundland, and the other near Long Pond in Conception Bay on the Avalon Peninsula, Newfoundland. In each area multiple samples were taken with both sampler types, and the samples processed immediately to establish the types and quantities of marine organisms that were present. Species identification is expected to be complete by late August.

Jan 1, 1994

By Renee Grogan

"An environmental impact assessment (EIA) of a deep sea mining project typically describes the environmental baseline, impacts of the project to the environmental values, and proposed management techniques. Comprehensive EIAs also consider the impact of the mining project on existing industries, including deep sea fishing. However, few projects to date have included other industries in the EIA process in more than a cursory manner, due to the confidentiality of the process, conflicting priorities, and bureaucratic limitation. However, if the United Nations Sustainable Development Goals (particularly Goal 17: Collaboration) are to be achieved, a new way of thinking will be necessary for deep sea mining projects, starting with collaboration at the very beginning of the project life cycle.STRUCTURE OF PRESENTATIONThis presentation will be in the format of an oral (20 minute presentation).The presentation will cover the process of inter-industry collaboration throughout the life cycle of a deep sea mining project, drawing on historical and existing examples, including that of the Chatham Rock Phosphate Project in New Zealand."

Jan 1, 2017

By William J. Scott

In the last two years, C-CORE has developed a new seabed sampler directed specifically at obtaining samples from hard or compacted bottoms such as are typical of marine placer deposits. Samples are required for appraisal of concentrations of saleable commodities, and for determination of levels of biological indicators in the deposits. Recently C-CORE and the University of Victoria have been comparing the performance of the Scott/C-CORE sampler with that of the Van Veen sampler often used for biological sampling. Initial trials of the Scott/C-CORE sampler in 1992 at the WestGold mining site, Nome, Alaska, were described by Jewitt et al. at the 1993 UMI. Since that time the sampler has been modified to prevent overfilling, and to limit turbulent flow of water across the top of the sampler buckets when the sampler is recovered with partly-open buckets. The modifications included shoes to prevent sampler overfill, and flexible rubber shielding over top and sides of the sampler to prevent water circulation. Samples have been taken with both samplers in two field areas, one at Pine Cove, Baie Verte, Newfoundland, and the other near Long Pond in Conception Bay on the Avalon Peninsula, Newfoundland. In each area multiple samples were taken with both sampler types, and the samples processed immediately to establish the types and quantities of marine organisms that were present. Species identification is expected to be complete by late August.

Jan 1, 1994

By Laura Moore

The southern shoreline of Monterey Bay, extending from Moss Landing to the Monterey Peninsula, consists of sandy beaches backed by an extensive Flandrian and pre-Flandrian dune complex. This length of shoreline, proximal to areas of urban expansion, is currently being considered for development. For this reason, it is extremely important to understand the variability of beach and dune position along this stretch of coast through time. Previous studies of southern Monterey Bay have documented relatively high erosion rates of 2-8 ft/yr due to a net deficit in the sand budget. Although the sediment transport system in this region is not well understood, estimates for the sediment deficit in southern Monterey Bay range from 200,000 to 1,500,000 yd3/yr. A possible cause of the erosional regime in the southern bay is the removal of sediment by coastal sand mining operations. Based on agency reports and mining permit applications, approximate volumes of sand removed by mining range from 300,000 to 450,000 yd3/yr. These volumes are significant when compared with estimated values for the sediment budget deficit. The sand of southern Monterey Bay, a valuable commercial resource because of its hardness, roundness, amber color and range of usable grain sizes, has been removed from the surf zone, beaches and dunes of Marina and Sand City by four companies since 1906. Information regarding the cross-shore location of sand removal and the exact amounts of sand removal through time is proprietary and poorly documented. However, records documenting the time at which each company commenced and terminated mining do exist. This information suggests that the greatest amount of sand was removed between 1950 and 1968 when three mining companies were operating concurrently.

Jan 1, 1994

By S. Kim Juniper

Ocean observatory technologies permit uninterrupted, real-time observation of dynamic seafloor environments such as gas hydrate deposits and hydrothermal vent fields that are of both scientific and economic interest. Such observations enable new discoveries of linkages between physical, chemical and biological processes and could permit continuous monitoring of environmental variables during mining operations. Ocean Networks Canada operates the NEPTUNE and VENUS cabled observatories in the Northeast Pacific Ocean. The offshore NEPTUNE observatory supports instruments at two gas hydrate sites on the continental margin off Vancouver Island, and in the hydrothermal vent fields of the Endeavour segment of the Juan de Fuca Ridge. The primary focus of the gas hydrate field observations is to understand the dynamics of the growth and stability of outcropping and sub-seafloor hydrate deposits. Outcropping hydrates at 840 m depth in Barkley Canyon have been monitored for the past 3 years with a mobile instrument platform known as Wally, which is operated over the Internet by a research group in Germany. This tracked vehicle carries standard oceanographic sensors, acoustic current metres, cameras and methane sensors. Data indicate a relationship between degassing of hydrates and tidal currents. In 2012-2013 two high-resolution sonar towers were added to the hydrate field to provide precision tracking of Wally and to monitor volume changes in the outcropping hydrate mounds. A large subsurface hydrate deposit occurs at the Clayoquot Slope site, where bottom depth is 1260 metres. Monitoring instrumentation is currently being established at this location. Gas bubble release from this deposit is being monitored by a sector scanning sonar mounted on a

Sep 14, 2011

By Demoor Damien

"The exploitation of marine resources has enjoyed renewed interest with a completely new sector, that of the Deep Sea Mining of mineral resources in the seabed, that is now gaining momentum. Nevertheless, the significant environmental constraints represent a challenge for initiating these new activities, whether this is in terms of the knowledge of the concerned ecosystems or in terms of monitoring and minimizing the impact of these new activities. This paper presents 2 technologies that aim to respond to the expectations of the stakeholders in this area. The first consists of the real-time monitoring of installations/operations and their impact on the environment using the most modern underwater technologies and especially long-term deployment AUV based on AUV docking station solution and autonomous long term observatories. The second consists of a membrane allowing the confinement of an area, the reduction of the emission of particles in suspension and noise reduction.IntroductionDeep ocean environments have been explored since the mid-1800s. As the land-based reserves of hydrocarbons and minerals become depleted, increasing numbers of resourcebased projects are being proposed for shallow then deepwater environments. Two distinct resource sectors have recognized the potential commercial value of working in shallow and deepwater environments – Oil and Gas and now Mining."

Jan 1, 2017

By Jan Willem van Bloois

IHC Merwede is world market leader in the construction of specialist dredging equipment; it is a company with a rich history. The Netherlands is a coastal western country for which water management is a very important issue. Without the enclosure of the coastal areas with dikes and dunes almost two third of the Netherlands would be flooded. These activities are mostly performed by the dredging industry and are the foundation of the dredging industry as it is today. Besides land protection this industry also carries out infrastructure maintenance and performs land reclamation projects. In essence the dredging industry is specialized in horizontal excavation activities and operations in shallow waters with the purpose of gathering bottom sediments and disposing it at a different location. The development is that the activities are moving to deeper waters to a depth of up to 150m. A few years ago IHC Merwede received a request to perform the shallow water excavation techniques at a depth of approximately 2000 meters for the deep sea mining market. In response to the increasing number of requests for deep sea dredging and mining application solutions, IHC Merwede combined all of its activities in this sector to create a new, specially equipped operational unit, IHC Deep Sea Dredging & Mining (IHC DSDM).

Jan 1, 2010

By David Gwyther

There is increasing recognition that in order for a development project to proceed successfully, it must first obtain a ?social licence to operate? from concerned stakeholders. Obtaining this ?licence? is in many ways a separate process to the legal one which involves, among other things, submitting an environmental and social impact assessment (ESIA) to the appropriate regulatory authority for review. Essentially, the function of an ESIA is to present a project?s technical, financial and social benefits, together with its environmental and social impacts in a transparent way to enable regulators to make an informed decision about whether the benefits outweigh the impacts, and thus whether or not the proposed project should proceed. The focus in the early days of ESIAs was primarily technical and was aimed to answer two fundamental questions: ?Can the project be built?? and ?Can we minimise impacts to a level that is acceptable to the community?? Basically, the ESIA process was a technical test of competence, but more recently, ESIAs have become much more than this. The main ESIA risk is now more akin to a test of a project?s legitimacy ? i.e., with more weight placed on the social licence, or the political test of moral authority ? with the process involving stakeholders from multiple backgrounds and disciplines, including some anti-development NGOs/civil society groups with their views on mining, (particularly in developing nations), often already pre-determined. Within the backdrop of this potential maelstrom, now enter a proposal for a new industry (such as deep sea mineral extraction).

Jan 1, 2011

By Alexander Malahoff

An international research team working through the Hawai?i Undersea Research Laboratory (HURL) undertook a bold challenge to explore the chemistry, geology, mineral formation and superheated hydrothermal vents of the Kermadec Island Arc. With the mothership, R/V Ka?imikai-o-Kanaloa, scientists from six research institutions explored the active submarine volcanoes stretching over a line of volcanoes 1,000 miles long between Samoa and New Zealand. The expedition left Hawaii on the 18th of March 2005 and returned on the 5th of August having covered a distance of 10,000 miles between Hawaii and New Zealand. Scientists from the USA, New Zealand and Germany used the HURL submersibles, Pisces IV and Pisces V, as well as the remotely-operated vehicle RCV-150, aboard the R/V Ka?imikai-o-Kanaloa to dive into active volcanoes to water depths of 2,000 meters. Scientists from New Zealand, the USA and Germany conducted 41 dives on the previously unexplored (from manned submersibles) submarine volcanoes. Ten active volcanoes were explored during this time. Hundreds of specimens of new and unusual marine life, water chemistry, extremophile microorganisms, mineral formations and volcanic rocks were collected during this expedition with the two submersibles and the ROV. Bizarre natural events, such as the oozing of hot liquid sulfur from the ocean floor onto the skids of the submersible were observed. Carbon dioxide gas was observed profusely streaming into the seawater from the volcanoes, making these one of the greatest contributions to hot house gasses entering the atmosphere.

Jan 1, 2005

By U. Schwarz-Schampera, P. Stoffers

The main characteristics of the 2545 km Tonga-Kermadec subduction system are the subduction of the Pacific Plate and its sedimentary cover in the Tonga-Kermadec trench and the extension and rifting of the lithosphere behind the active island arc in the Lau basin - Havre Trough back-arc systems. The subduction of the Louisville Seamount chain at 25.6°S affects the tectonic and volcanic system and separates the island arc into the Tonga arc and the Kermadec arc, respectively. To the west, a Miocene island arc is represented by the Lau-Colville ridge. The crustal extension between the Lau-Colville and the Tonga-Kermadec ridge started at about 6 Ma, and induced their separation and the onset of the southward rifting since about 5 Ma. Characteristics of the Tonga-Kermadec arc system include (i) the fourthfold decrease of the subduction rate from 24 cm/a in northern Tonga to 6 cm/a in the southern Kermadec trench, mainly north of 23.5°S; (ii) the development from fast spreading in the Lau basin (16 cm/a) to slow rifting (2 cm/a) in the southern Havre Trough with the transition from spreading to rifting at 23.5°S; (iii) variations in the composition and the volume of the subducting sediments and rocks (detritus from the Samoan hotspot at the northern Tonga arc; the aseismic Louisville ridge at the southern Tonga arc; increasing terrigenous sediments from New Zealand at the southern Kermadec arc); (iv) a number of active volcanic centers younger than 1 Ma and characterized by significant shallow submarine hydrothermal systems.

Aug 24, 2006

By Daniel E. Walsh

The recovery of most minerals, which are amenable to gravity concentration, is standardly determined by accurate sampling and assaying. .With respect to particulate - gold ores, sampling and assaying are still the convention, but the accuracy and reproducibility of these operations are much discussed and debated points. Evaluation of gravity concentrators by conventional sampling and assaying techniques is very time consuming, costly and may introduce a large amount of uncertainty into the results due to the particulate nature of placer gold. These problems are not unique to placer gold ores and apply to any low grade ore with particulate values. A gravity concentrator evaluation process developed by MIRL employs the use of neutron activated gold (198Au) and radiation detection circuits which monitor the concentrator's product pulp streams. Concentrator recovery is determined from the ratio of the number of gold particles detected as passing into the concentrate to the total number of gold particles detected over all monitored pulp streams. This system eliminates the experimental errors introduced by sampling, sample reduction, and assaying and allows recovery to be evaluated for gold particles of specific sizes, shapes, and flatness. This system enjoys its greatest utility where a large number of tests are to be run in order to evaluate a concentrator over a variety of operational settings, i.e. factorial designs, and allows accurate testing of concentrators operated in closed circuit systems. Beginning in 1984, MIRL conducted radiotracer studies of unit processes, which included jigging, static wedge wire screening, elutriation, and concentration with compound water cyclones.

Jan 1, 1989

By Luc Rombouts

The resources and reserves calculation of marine diamond deposits should be based on a systematic sampling grid. The distribution of the sample grade results tends to be very skew and has a large variance. A bias is easily introduced due to the fact that the grade distribution of the samples is very different from the grades of the area of influence. The temptation is always there to extrapolate the highest grade samples simply to their area of influence. If this is done, the higher grade areas will be systematically overestimated, while the lower grade areas will be underestimated. Such a bias should surely be avoided by weighing the sample grades in such a way with their neighbours, so that the estimated grades have a similar distribution as the grades of the blocks. The grade distribution of small mining blocks tend to be lognormal-like. If the coefficient of variation is known, i.e. the standard deviation divided by the mean, then the grade distribution of the small mining blocks is relatively well-defined. The distribution of the diamonds within the deposits can be simulated, based on the histogram of the sample results and on the semivariogram. The diamonds tend to cluster in trapsites. From the semivariogram and the histogram, the average size and spacing between trapsites, and the grade distribution within the trapsites, can be calculated using the model of the General Family of Discrete Distributions. Using such a simulated deposit, the grade distribution for different block sizes can be obtained. The grade distributions become more lognormal-like with increasing block sizes, as the trapsite effect is reduced.

Jan 1, 1998

By Chan Min Yoo, Jung-Keuk Kang, Wonnyon Kim

Recently high-resolution paleomagnetic age determination of ferromanganese crust in less than millimeter scale has been successfully carried out using a superconducting quantum interference device microscopy magnetometer (SMM). However, it has not been clearly identified how the crust is keeping ancient geomagnetic field records. Here we try to identify magnetic mineralogy of the crust obtained in the Magellan Seamounts, the West Pacific (~20 °N). As a record, age of the crust used in this study is extended to ~10 Ma at ~40 mm depth and ~28 Ma at ~100 mm depth, respectively, based on the combination approach of SMM measurements, Be-isotope and Co-chronology. Thermal demagnetization revealed a Curie temperature of ~560oC, corresponding to (titano)magnetite. Component analysis of isothermal remanent magnetization identified a presence of two types of magnetite. Measurements of first order reverse curve showed a dominance of non-interacting single-domain magnetite, which is one of the intrinsic feature of biogenic magnetite. Although most of the magnetic particles on transmitted electron microscopy are covered by amorphous Fe-Mn minerals, some are observed as a prototype of biogenic magnetite showing a chain of ~10 nm sized magnetite cubes. However, a magnetite signal (i.e., Verway transition at ~ –120 oC) was not detected in low-temperature treatment probably due to surface oxidation of magnetite. Contribution of interacting magnetite of detrital origin is <30% throughout a crust. Interestingly, contribution of detrital magnetite is almost three times higher since ~10 Ma. At this boundary, a growth rate of the crust is double up and flux of other detrital signals, including Al, Mg, Ti and Zr, are also increased.

Jan 1, 2017

By Robert M. Owen

Recent advances in coring technology and in the development of shipboard and/or in situ geochemical geochemical analysis systems have greatly improved our ability to collect and analyze exploration samples, particularly for marine placer exploration programs. The potential benefit of these improvements cannot be fully realized, however, until we also develop more efficient methods of data reduction and interpretation. Specifically, there is a need to provide prospectors with rapid and useful interpretations of the raw geochemical data so that they can exploit promising results and otherwise optimize the exploration program while the exploration vessel is still at sea. The goal of this project has been to identify and/or develop computer software which is capable of making the necessary data reduction calculations and which can be run on conventional desk-top computers. All work on this project has been supported through a research grant from MMTC-CSD to The University of Michigan. The first stage of this effort involved an evaluation of commercially available (i.e., "off the shelf") software to determine its suitability for use in marine placer exploration applications. Various commercial software packages, each purportedly capable of making different types of statistical and/or mathematical calculations, were tested by evaluating their performance in handling geochemical data sets representative of actual marine placer locations. These data sets include the positions and results of chemical analyses of suites of sediment samples collected from areas of known or suspected marine placers along the Bering Sea coast of Alaska. The evaluation of each commercial program involved a comparison between the results obtained from using the test program

Jan 1, 1991

By J. Robert Woolsey

A unique concept for a self-cleaning filter system has been designed and constructed which utilizes acoustic energy, coupled hydraulically with a subject liquid media, and a fine mesh screen to perform the following: 1. separation of solid suspended particles from a host liquid through the breakdown of surface tension; 2. enhanced filtration of liquid fraction from the solids fraction to specified limits, retaining a specified size range of solids, and; 3. continuous cleaning of screen, preventing screen blinding and promoting a continuous filtration process. The concept is the product of a cooperative program between the Marine Minerals Technology Center, Continental Shelf Division, and the Moscow State Mining University. The physical principals involved in the separation, filtration, and screen cleaning processes primarily relate to the characteristics and properties of the applied acoustic energy and the influence of this energy on the solids/liquid mixture. The acoustic energy introduced to, and acting on and throughout, the whole volume of the solids/liquid mixture, within the vessel body at any given time induces hydraulic pressure waves, which may be further described in simplest form as positive and negative semiperiods (which may or may not be equal in amplitude or period) of the basic wave forms. The processes involved may be considered in two phases. The first phase relates to the process of separation in which the acoustically induced force of acceleration manifests as vibro-agitation (thresh- old of cavitation) and possibly cavitation is the primary factor in the breakdown of surface tension between the solid particles and suspending liquid; i.e. water. In the case of compressible organic solids, the separation of liquid by squeezing may also be a factor.

Jan 1, 1994

By Thomas Kuhn, Anna Wegorzewski

"INTRODUCTIONPolymetallic nodules from the Clarion and Clipperton Zone (CCZ) within the equatorial NE Pacific Ocean show high concentration of economic important strategic metals such as Ni, Cu, Co, Mo and Rare Earth Elements (REE). The content of those metals in nodules is depending on (i) the supply during individual growing periods, (ii) the environment conditions as well as (iii) on different manganese minerals, which occur in nodules. The incorporation of the metals can vary within the structure (incorporated into the structure / over vacancies of the structure) and this can be relevant for the further metallurgical treatment.Mineralogy of Mn-nodules from the CCZ and the incorporation of metalsManganese nodules consist of nm to µm thick layer growth structures (LGS) of different genetic origin (hydrogenetic/suboxic-diagenetic). Those LGS form due to the precipitation of Mn-and Fe-(oxy) hydroxide colloids from the oxygen rich near-bottom water and/or pore water (hydrogenetic growth; Halbach et al., 1988) or from suboxic (depleted in O2 <5µmol O2/l; Hein and Koschinsky 2013)) near-bottom water/pore water (suboxicdiagenetic growth; Halbach et al., 1988; Wegorzewski and Kuhn, 2014).In general, metals dissolved in seawater will be adsorbed and complexed on the oxide surfaces according to their different surface charge. The surface charge of the Mn-Fe (oxy) hydroxides depends on the pHzpc (zpc: zero point of charge). In seawater dissolved hydrated cations (Ni2+, Cu2+, Co2+) are adsorbed preferentially on the negatively charged Mn-oxide (MnO2 -) surface (pHzpc 2.8). In contrast, negatively and neutrally charged complexes (e.g., Ti(OH4); REE(CO3)2 -, MoO4 2-) are adsorbed on the surface of Fe-oxy hydroxide colloids (FeOOH+) which have a slightly positively charged surface (pHzpc 8.5; Stumm and Morgan, 1981; Koschinsky and Halbach 1995)."

Jan 1, 2017

By Robert M. Owen

The rare earth elements (REE1s; atomic number 57 -71) exhibit a coherent chemistry, are widespread in nature, and tend to occur in characteristic concentrations in different geochemical phases. Because of their predictable chemistry, the REE&apos;s-are highly useful as indicators or tracers of geochemical processes, and are often used as such in investigations of the genesis of terrestrial ore deposits. However, analogous applications of the REE&apos;s to the study of marine mineral deposits have been constrained by our limited understanding of the marine geochemical cycle of these elements. For example, a continuing area of uncertainty in this regard involves the so-called "REE Mass Balance Problem." This problem refers to the fact that detailed geochemical mass balance calculations typically predict a significant imbalance for the REE&apos;s; i.e., the calculations predict that REE removal rates from seawater are 11-18 times greater than their input rates. Yet all other chemical considerations indicate that the REE budget should be roughly in balance. Recent studies at The University of Michigan suggest the solution to this problem lies in understanding the the role of seafloor hydrothermal activity in the marine budget of the REE&apos;s. Geochemical analyses of hydrothermal sediments from two Pacific sites (East pacific Rise at 19°s and the Southern Juan de Fuca Ridge at 45°N) clearly show that the REE component of hydrothermal sediments is primarily acquired via scavenging from seawater. Iron oxyhydroxides, which form as precipitates when hydrothermal solutions are debouched onto the seafloor, are the active scavenging agent. Although the REE content of hydrothermal sediments generally increases with increasing distance from the rise crest, this increase is especially pronounced for sediments deposited below the lysocline,

Jan 1, 1989

By Seung-Kyu Son

Environmental properties of the northeast Equatorial Pacific along 131.5 degrees west, between 5 degrees and 13 degrees north latitude, were investigated in association with changes in water column structures during the summer seasons of 1998 and 1999. Climatic disturbances such as El Nino and La Nina, should have affected this area during the study period. In 1998, a thermocline where temperatures rapidly decrease with depth, was formed at 90~110 m water depth. However, in 1999, a very fluctuating thermocline was observed with latitudes. As a result of changes in the water column structures, biological and chemical environment also showed fluctuation parallel to the changes in other physical parameters. Inorganic nutrient depleting areas, especially for nitrate+nitrite and phosphate, or oligotrophic regions were extended down to approximately 100 m depth, which coincided with the surface mixed layer depth. In the euphotic zone, depth integrated nitrogen (N) and phosphorus (P) values were 34 g-N/m2 (grams of Nitrogen per square meter of sea floor), 7 g-P/m2 in 1998 and 130 g-N/m2, 18 g-P/m2 in 1999, respectively. The results indicated that nitrogen (96 g-N/m2) and phosphorus (11 g-P/m2) are supported by up-welling and down-welling phenomena with convergence and divergence in the study area. Biological parameters in the water columns were largely determined by the physico-chemical environmental parameters. Subsurface chlorophyll maximum layers were coincided with the formation of seasonal thermocline. Copepods were the dominant group of zooplankton community at three sampling stations (N5, N6, N10) terms of abundance, which was the same results of previous surveys for the past 3 years. Among copepod populations, Oncaea sp., Oithona sp. Clausocalanus sp., Acarocalanus sp. and juvenile copepodites were dominant Appendicularians, foraminiferans and radiolarians were also dominant. To investigate diel vertical migration pattern of zooplankton, repeated samplings from the water depth of 0~50m and 50~200m were conducted at KODOS (Korea Deep Ocean Study) area before and after sunrise. Zooplankton abundance was slightly higher after sunrise than before sunrise in the surface layer. Chlorophyll-a concentrations were relatively low as the concentration of sediment increased in most experiments possibly due to a decrease of grazing pressure of microzooplantkon such as ciliates, which is the efficient grazer on small-sized phytoplankton. Because copepod predation on microzooplankton may be prevented by the high concentration of sediment, resulting in lower grazing pressure on small-sized phytoplankton. The results obtained during the baseline study as a part of KODOS project since 1998.

Jan 1, 2001

By Kaihui Yang

Volcanogenic massive sulfide deposits are generally considered to have been formed by hydrothermal fluids that leach ore metals out of footwall rocks. However, the necessity for a metal-rich magmatic component in the ore-forming fluid of "giant" ore deposits has been debated over the decades. The solution to this issue is important not only for metallogenic models but also for the mineral exploration. In the hydrothermal leaching model, massive sulfides at mid-ocean ridges are deposited from hydrothermal fluids containing 80 ppm Fe, 6 ppm Zn, 2 ppm Cu, 350oC, and 0.7 g/cm3 density (average data for 21oN East Pacific Rise). A simple calculation demonstrates that such a dilute fluid is unlikely to have been responsible for the formation of the largest ancient massive sulfide ores of greater than 100x106 tonnes, such as Kidd Creek, Brunswick No. 12, Neves Corvo, and Rio Tinto. For such a deposit consisting primarily of pyrite, sphalerite, galena and chalcopyrite (other minerals, including gangue, might account for an additional 10-20%) and even assuming 100% precipitation and retention of the sulfides, more than 790 km3 of vent fluid would be required. For typical water-rock reaction ratios of about 2, this fluid would have to have reacted with about 395 km3 of rock to acquire its metals by conventional leaching processes. This estimate, however, conflicts with the observation that even a giant massive sulfide ore body is usually underlain only by a few cube kilometers of obviously altered rocks. Moreover, this model is not consistent with the observation of hanging wall alteration in many large massive sulfide deposits. The close spatial association between massive sulfides and volcanic rocks, in both ancient and modern sea floors, suggests that direct magmatic contribution should be taken into account in the genetic model. Magmatic fluids, capable of carrying abundant ore metals and volatiles and escaping from magma by depressurization, are well known from modern active volcanoes on land. High concentrations of metals occur in CO2-rich magmatic fluid trapped in felsic volcanic rocks nearby large presently-forming VMS deposits in the eastern Manus Basin (Pacmanus, Suzette) and also in the footwall rocks of Ordovician giant Brunswick #12 deposit in the Bathurst district, New Brunswick. Only 1% of such metal-rich magmatic fluid mixed with heated sea water, that has leached its metals from rocks, would contribute 85% of the total metals to form an orebody. Such magmatic fluids are most likely to be formed from volatile-rich felsic magmas that are prevalent in back arcs, and, if added to the normal circulation system, the fluids could be responsible for the formation of "giant" ore deposits. If this is true, then the study of magmatic fluids in the seafloor volcanic rocks may provide criteria for the exploration of large ore deposits.

Jan 1, 2011

By Rahul Sharma

Although, mining of minerals such as polymetallic nodules and sulphides from the deep sea floor has been delayed due to the combination of factors such as current availability of Cu, Ni, Co, Mn (and other metals) on land and their fluctuating prices; these deposits are still considered as the alternative source for metals in the 21st century. Exclusive rights for exploration in the ?Area? (beyond the national jurisdictions of any country) given to eight countries and consortia by the International Seabed Authority and the estimated resource of 300 million tonnes in a typical area of 75,000 km2 is expected to yield about $17.5 billion (at December 2008 metal prices) in 20 years life span of a single nodule mine-site. In order to recover 3 million tonnes of nodules, an area of 300 sq km only will be mined annually (i.e. <1 km2/day) for an optimum abundance of 10 kg/m2. However, during mining, large quantity (22 tonnes/day) of sediments associated with nodules would be resuspended that could lead to certain environmental impacts on the benthic ecosystem. Several small-scale benthic impact experiments in the Pacific and Indian Oceans, have given some insight into the possible environmental impacts and the restoration processes, but the possibility of extrapolating these findings to a commercial mining scale remains an issue to be considered. An estimated capital expenditure of $1.05 billion and operating expenditure of $4.2 billion for a single deep-sea mining venture will have to be weighed against the availability of mineral ores on land as well as the metal prices in the world market. None-the-less, development of technologies for mining and metallurgical processing, as well as formulation of regulations and guidelines for potential ?contractors? to mine these minerals have been progressing consistently. These coupled with recent efforts by certain ?entrepreneurs? to initiate mining of seafloor massive sulphides in the EEZ of certain countries, indicate the continuing interest and support the perception that such deposits could well be the future sources of metals. This paper analyzes the current status and discusses the economic, environmental, and technical issues that need to be addressed for sustainable development of deep-sea minerals.

Jan 1, 2010