Sediment-hosted zinc potential in Greenland. Reporting the mineral ressource assessement workshop 29 November - 1 December 2011

Lars Lund Sørensen, Bo Møller Stensgaard, Kristine Thrane, Diogo Rosa, Per Kalvig

Publikation: Bog/rapportRapport (offentligt tilgængelig)

Abstrakt

Quantitative information on mineral resources is required among decision makers from governmental agencies and the private mining sector. In response to this, in 2002, the United States Geological Survey (USGS) initiated the project ’Global Mineral Resource Assessment Project’ (GMRAP), with the primary objective to identify the principal areas in the world with potential for selected undiscovered mineral resources, in the uppermost one kilometre of the crust, using available compiled information and modern quantitative statistical models.

The GMRAP is being conducted on a regional-multinational basis for selected deposit models and commodities, and on a global scale, coordinated by the USGS, by compiling information from the regional assessments. The Greenlandic Bureau of Minerals and Petroleum (BMP) and the Geological Survey of Denmark and Greenland (GEUS) are participants in the GMRAP-project and hosted a GMRAP workshop on sedimentary-hosted copper in 2008 (Stensgaard et al. 2011). Subsequently, additional assessment workshops have been undertaken at GEUS and BMP on other commodities and mineral deposit models. These workshops have however not been carried out under the auspices of the official USGS GMRAP program, but have, when possible, utilised the standard rules and methodologies set by the GMRAP program.

The assessment workshop for 2011 was chosen by BMP and GEUS to be focused on the potential for undiscovered sediment-hosted zinc deposits in Greenland. The two mineral deposits that were assessed Sedimentary Exhalative (SEDEX) and Mississippi Valley Zn-Pb-Ag deposit types.

The workshop applied the standardised methodology, defined for the GMRAP assessments involving the ‘Three-Part Form’ assessment approach, including, (i) delineation of tracts of land where the geology is permissive for sediment-hosted zinc deposits to form; (ii) selection of grade and tonnage models appropriate for estimating grades and tonnages of the undiscovered sediment-hosted zinc deposits in each tract; and (iii) estimation of the number of undiscovered sediment-hosted zinc deposits in each tract consistent with the grade and tonnage model.

Based on a discussion and evaluation of all available information and data for defined tracts found to be permissive for sediment-hosted zinc, the individual members of the assessment panel provided bids at different confidence levels on how many deposits of a certain size and a certain grade would be possible to find, under the best possible circumstances. After the individual bids, these were discussed and argued until the assessment panel agreed on a consensus opinion on the numbers of undiscovered sediment-hosted zinc deposits. The consensus bid was then used as inputs to a Monte Carlo simulation computer program (EMINERS developed by the USGS), combining the probability distributions of the estimated number of undiscovered deposits, the grades, and the tonnages of the selected model to obtain the probability distributions for undiscovered metals in each tract.

Sedimentary basin environments constitute approximately 40% of Greenland’s ca. 410,000 km2 ice-free land area, and several of the basins host zinc mineralisations. The workshop considered two deposit types; Sedimentary Exhalative (SEDEX) type and Mississippi Valley type (MVT) that accounts for more than 50% of the world’s known zinc reserves. A third type; the Volcanic Massive Sulphide type (VMS), that accounts for around 30% of the world’s zinc reserves, were not assessed at the workshop due to lack of time.

In the course of the workshop a total of 23 estimations of undiscovered sediment-hosted zinc deposits in defined tracts were assessed in strict accordance with the guidelines for the ‘Three-Part Form’ assessment approach. The assessment made it obvious that only very scarce information is available for most of the tracts as many areas only have seen limited to none exploration and investigation campaigns.

The expected number of undiscovered SEDEX and MVT deposits in Greenland was estimated to be 8 and 5 respectively with a statistical simulated estimated total mean of undiscovered zinc resources of 24.8 million tons (Zn metal).

These estimates should be used with great caution and should be regarded as an uncertain statistical estimate that reflects the present level of knowledge and investigations that have been undertaken in the assessed tracts. To a large degree, it also reflects the confidence level of the estimated number of undiscovered zinc deposits within the tracts that have been assessed.

The circumstances that the large majority of assessed tracts lack sufficient information and data for an absolute assessment, should give rise to even more cautions when using the estimated zinc resource value. New information, new discoveries, new investigations etc. within a tract should thus, if possible, be taken into account when evaluating an area, as this could either decrease or increase the estimated value.

The bids on undiscovered zinc deposits made by the assessment panel team at different confidence levels and the increase in numbers from one confidence level to another are perhaps the most important information to consider. Deviations from one level to another reflect the level of knowledge about the various areas and the overall assessment of the potential and prospectivity within the areas. Also, deviations between various team members of the panel, may indicate a different level of knowledge amongst members or a difference in rational behind the bids.

The assessment panel team agreed that the largest potential for large grade-tonnage deposits of the SEDEX zinc type was within (i) the trough sequence within the Franklinian Basin in North Greenland, (ii) the Etah Group of the Inglefield mobile belt in North-West Greenland, (iii) the Rivieradal and Hagen Fjord Groups in the Hekla Sund Basin in eastern North Greenland, and (iv) the Foldvik Creek successions in the Jameson Land Basin in central East Greenland.

The biggest potential for MVT-type zinc deposits was agreed to be within (i) the carbonate shelf-platform of the Franklinian Basin in North Greenland, (ii) the Foldvik Creek succession in the Jameson Land Basin in central East Greenland and (iii) the Mârmorilik Formation of the Karrat Group in West Greenland.
OriginalsprogEngelsk
UdgivelsesstedCopenhagen
ForlagGEUS
Antal sider184
DOI
StatusUdgivet - 19 sep. 2013

Publikationsserier

NavnDanmarks og Grønlands Geologiske Undersøgelse Rapport
ForlagGEUS
Nr.56
Vol/bind2013

Emneord

  • Greenland

Programområde

  • Programområde 4: Mineralske råstoffer

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