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Project Progress

Vertical and horizontal excavations at the Lupin gold mine in northern Canada allow access to a 500-meter thick permafrost/rock environment overlying a methane-bearing brine/rock environment. Groundwater, gas, and rock samples were collected by IPTAI scientists during two field trips to Lupin (Figure 1). Filtered groundwater samples collected in 2004 did not yield sufficient biomass for DNA characterization via polymerase chain reaction (PCR) amplification of small subunit ribosomal DNA (16SrDNA). Consequently, filtered samples collected in 2005 employed in-line filters capable of handling higher flow rates and exposure for longer periods of time (3 days). As a result, we now have successfully amplified the 16SrDNA from two of the boreholes and are continuing to work on samples from four other boreholes. Initial results indicate a diverse bacterial community. PCR products have been submitted for sequencing. Archaeal 16SrDNA is not as abundant as bacterial, but we’re continuing to work on extraction of any archaeal signal. We have hopefully succeeded in filtering sufficient biomass for metagenomic analysis of the deep-subsurface environment at Lupin.

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Microbiological samples from 2004 yielded a diverse population of aerobic (possibly facultative) bacteria and a sulfate reducing anaerobe, but no Archaea. Samples from 2005 have yielded several sulfate reducing anaerobes and fermentative anaerobes. The enrichment cultures appear to be monophyletic and their PCR amplified 16SrDNA have been submitted for sequencing.

Stable sulfur isotope analyses have been performed at Indiana University for both dissolved sulfate and sulfide. Initial isotopic results indicate that most of the brine samples exhibit little microbial fractionation with the exception of brine from one borehole which also yielded a sulfate reducing anaerobic enrichment.

Carbon and hydrogen isotopic analyses have been completed for gas samples collected in 2004. It appears that methane, ethane, propane and butane (C_1-4 hydrocarbons)have a thermogenic signature, although a mixture of methanogenic and abiogenic cannot be excluded. Additional samples were collected in 2005 in order to verify isotopic characterization of Lupin gases. If the origin is thermogenic, then the C_1-4 hydrocarbons at Lupin are Archean/Proterozoic in origin and their formation coincides with the timing of the last major orogenic episode. A thermogenic origin is quite unusual as previously published analyses of C_1-4 hydrocarbons from the Canadian Shield all suggested an abiogenic origin. Isotopic analyses indicate that microbial methane is not dominant in the Lupin gases.

Helium gas analyses indicate subsurface residence times that are on the order of ~100 million years at least. Complete noble gas isotopic analyses have been completed by Ian Clark of the Univ. of Ottawa and his analyses will be able to provide a more accurate determination of isolation time. This age, however, is much greater than the 10 kyr estimated age of the permafrost.

Anion and cation analyses of last year’s and this year’s samples are consistent with analyses performed by the Finnish Geological Survey for the past 4 years and indicate that the geochemical environment, in particular the redox state, has remained stable over this period of time. We infer that mining activities have not perturbed the brines isolated in fractures at Lupin. When these results are compared with extensive data set collected from South African gold mines in the Witwatersrand Basin, the similarities are quite remarkable, particularly considering that the depth range of the Lupin boreholes is relatively shallow (less than 1.5 kilometers) compared to mines as deep as 4 kilometers below the surface in South Africa. It is significant, however, that the brines at Lupin are 35°C colder than the deep brines sampled in South Africa. It will be intriguing to see if the microbial communities at the Lupin mine are similar to those recovered from the South African gold mines.

A graduate student at Princeton University, Mark Davidson, is performing a “retentostat” experiment on a subsurface, thermophilic sulfate reducing bacteria, Desulfotomaculum putei. This experiment is designed to reproduce nutrient and energy levels of in situ conditions and then to slowly decrease these levels and examine the changes in the genes expressed, the changes in lipid composition and the changes in the sulfur isotope fractionation. We plan to continue these types of experiments using microbes cultured from sub-permafrost brines in northern Canada.

We have initiated discussions with mining officials at Wolfden concerning the acquisition of permafrost rock cores at the Ulu gold mine which is located ~100 km further north of Lupin. The Ulu mine is situated in a mafic/ultramafic Archean greenstone belt and has ~500 meters of permafrost. Wolfden is planning an extensive exploration drilling campaign for 2006 and it is our hope to piggy back on their effort with the acquisition of pristine permafrost/rock samples for microbial and geochemical analyses. Penetrate into the underlying environment is necessary to determine if a gas-bearing brine is present beneath the permafrost at Ulu and to assess if biogeochemical signatures of sub-permafrost brines are similar at Ulu and Lupin. To this end we have prepared and submitted a proposal to NAI where we are requesting funds to cover the cost of this drilling campaign.

Highlights

• Successful recovery and culturing of aerobic and anaerobic microbes from brines at depths from 800 to 1100 meters below the surface in northern Canada.
• Brines present beneath 500-meter thick permafrost were filtered and yielded sufficient DNA for PCR and sequencing of cold-tolerant, deep-subsurface microbes.