A burgeoning interest in seafloor mineralization from many different viewpoints ranging from scientific research and conservation groups to commercial and national organizations was the original impetus for InterRidge forming a Seafloor Mineralization Working Group (SMWG) in 2008. While fundamental scientific research issues are at the core of the working group’s mission, it was also a vehicle to allow the scientific community to bring a unified voice to issues facing the discovery and use of metal-rich seafloor mineral resources. The primary focus of the SMWG has been on polymetallic seafloor massive sulfide (SMS) deposits that form at hydrothermal vent systems found along the midocean ridge and back arc spreading systems of the world. During the past two years the International Seabed Authority (ISA), the UN body that has jurisdiction over “the area” of seafloor beyond national boundaries, has presented and gained approval for regulations governing “…the prospecting and exploration for polymetallic sulphides in the area.” These regulations allow for any ISA registered organization to file for leases in “the area” for the express purpose of mineral exploration. The ultimate goal of this exploration is for seafloor mining of metal rich SMS deposits, although regulations governing this activity remain to be defined. To date, two countries (China and Russia) have applied for, and gained, licenses for such exploratory licenses. Other countries are expected to follow suit soon. There is one active, publically-traded junior mining company (Nautilus) that has plans to begin SMS mining at its Solwara-1 prospect in 2013, which lies within the national jurisdiction of Papua New Guinea. In this latter case, a mining license has been sought and granted from the PNG government. The PNG government is also a stakeholder in this Solwara-1 project, raising potential questions about how independent environmental assessments and oversight can be achieved in an effective manner.
The SMWG began its tenure by organizing an InterRidge workshop and public forum at Woods Hole in 2009 to discuss and review the many issues concerning the exploration and exploitation of SMS deposits from multiple viewpoints and stakeholder positions. From an InterRidge perspective, a number of important scientific questions surround what we know and don’t know about how such mineralized systems form, their distribution along the midocean ridge and flanks, the magnitude, longevity, and potential flux estimates of heat and mass transport involved in seafloor mineralization, as well the processes involved in the ultimate fate of this mineralization. To date, most hydrothermal vent deposit studies have focused on active sites for the obvious reason that they are more easily detected with current technologies. These active vents, of course, also harbor unique biological communities often in extreme environmental conditions. At the Woods Hole workshop the SMWG developed three main questions to advance the scientific knowledge-base of SMS deposits:
What are the spatial controls on hydrothermal activity and SMS deposition?
What are the timescales for the evolution of SMS deposits?
What are the changes in biological communities that occur during the evolution of an SMS deposit?
A key question concerned the role, existence, and distribution of inactive deposits and what processes maybe involved in their preservation or destruction. Inactive deposits may become the first deposits mined at the seafloor. These questions remain relevant today and perhaps even more so in light of the recent interest in SMS following the issuance of the new ISA regulations. It would seem that it is in the express interest of InterRidge to continue to have a working group focused on questions concerning the formation and evolution of seafloor mineralization and the biological communities that inhabit them. In particular, so little is known about inactive deposits that it is imperative that science gets ahead of the commercial/national exploitation of these features before seafloor mining occurs and fully informed decisions need to be made on the progress of such activities. Since the workshop updated databases have been supplied to ISA on vent distributions and geochemistry. The SMWG has also been helping the InterRidge steering committee and representatives with information and feedback on issues brought forward by the ISA to InterRidge for comment. For example, the ISA recently asked InterRidge to identify areas of the midocean ridge system that it considered to be locations of sensitive scientific research areas that could potentially be considered as refuges or reserves exempt from exploitation.
The proposal here is to renew the 3-yr term of the Seafloor Mineralization Working Group and to tackle the issue of spatial and timescale controls on SMS deposit evolution, a key question in the SMWG summary. A workshop is in the planning stage by a German group led by Sven Petersen (a member of the SMWG) to host a workshop in Kiel, Germany in early 2012 to investigate the metal potential of a slow spreading ridge segment using high-resolution geological and geophysical mapping along with numerical simulations. The area under consideration is the TAG segment at 26N on the Mid-Atlantic Ridge, which has seen focused studies of the hydrothermal system as well as drilling but lacks a complete segment-scale context. It is envisioned that a multi-national approach at investigating this ridge segment would be a giant first step at quantifying segment scale mineralization processes along with the potential to define the role of inactive deposits. Important questions concerning the quantification of metal supply over geological timescales and spatial ridge segment scales can potentially be addressed. The scale of the project requires contributions and assets from multiple nations, which fits within the spirit of InterRidge in fostering interactions between nations on common research goals. From a biological perspective, the changes in faunal distributions away from centers of mineral deposition would inform other studies on the post-mining, post drilling and other post impact effects of faunal community recovery. A brief summary of the proposed Kiel workshop is attached. A modest contribution by InterRidge towards this conference would also help with planning and travel costs for participants.
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IFM-GEOMAR Workshop hosted by Sven Petersen and colleagues, tentative date: April 2012
The metal potential of a slow-spreading ridge segment
Investigations of submarine massive sulfide deposits as a possible metal resource are lacking several of the fundamental answers that need to be addressed. First of all, we do not know how much of the metal that is released by high-temperature venting over a given length of a ridge axis and over a specific geological time frame is actually deposited as massive sulfides. Recent estimates of the oceanwide metal potential of seafloor hydrothermal systems range from 530 x 109 tonnes Cu+Zn (Cathles, 2011) to 3 x 109 tonnes Cu+Zn (Hannington et al., 2010) 180 times less than the estimate of Cathles (2011). Hannington et al. (2010) argue that almost all of this is buried by off-axis sediments and will not be commercially available. It is therefore currently not known how much metal is bound to sulfides deposits or occurs as geochemical anomaly within sediments or is related to altered rocks in the upflow zone. Secondly, the tonnage calculations reported for most known seafloor deposits relies mostly on interpretation of visual surface information of the outcrop thickness and lateral dimensions, in most cases overestimating their size and tonnage. Additionally, exploration is usually performed by identifying chemical and physical tracers in the water column limiting the search to only active deposits within or close to the neovolcanic rift zone. Large inactive deposits have been found, sometimes by accident or by time-consuming TV-sled towing operations, further away from the rift, but techniques to identify such deposits on a regional scale are lacking. We also lack the ability to identify buried deposits (beneath sediments or lava) thereby underestimating the resource potential of explored areas. Systematic surveys including buried deposits from the ridge axis to 10's of kilometers away from the axis have never been performed limiting our interpretations to a small snapshot in time. We do not know, how much metal is deposited as sulfides over a time-span of, for instance, 10 mio years, along any given spreading ridge segment.
We therefore propose to investigate a section of the central Mid-Atlantic Ridge where known massive sulfide deposits (active and inactive) occur and were visual observation by submersibles suggests the presence of numerous other massive sulfide deposits partly buried beneath sediment further away from the ridge axis. The metal inventory of this ridge segment is still unknown despite the presence of the well-known 4 mio tonnes TAG deposit. With this project we hope to be able to budget, for the first time, the metal deposit inventory of a larger ridge segment in space and time by applying modern instruments (AUV) and adapting existing methods (EM, high-resolution 3D seismic studies, modeling) to the investigation of marine sulfide deposits. The presence of sulfide outcrops away from the ridge axis and the likelihood of more discoveries outside of the few submersible paths in this area make this segment a good site for testing regional-scale exploration technology for the discovery of blind deposits.
We want to use high-resolution mapping (AUV-based bathymetry, sidescan, photomosaicing) for large areas of the seafloor, for identifying favorable locations and seismic acquisition (deep towed and high resolution 3-D) as well as AUV-based magnetic and subbottom profiling surveys to locate buried deposits and estimate their thickness. If possible drilling information (lander-type or ROV-drill) will be used at a later stage to identify down-hole variability of the deposits that cannot be seen by geophysical tools. Where appropriate active and passive seismicity will be employed to image the upflow zones thereby providing valuable data for numerical modeling.
Sampling of the deposits and their host rocks either by ROV, TV-grab, dredging or drilling will gather information on the chemistry and will be used to estimate the metal content of the various deposits. This information will, together with the structural interpretation and the regional bathymetric datasets, feed into a 3-dimensional model of fluid flow in the crust along this ridge segment in order to constrain fluid pathways, the physicochemical conditions at depth and to ultimately budget the metal resource of this ridge segment over geological time scales.
