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Project Progress

The High Lake mining property (67° 22’ 47’‘ N, 110° 50’ 37’‘ W) is located in an Archean green stone belt (felsic and mafic volcanics) comprising a significant copper/zinc sulfide deposit and estimated to be frozen to a depth of about 440 meters. The deposit was originally discovered by recognition of the gossans, natural acidic drainage formations that result from the surficial oxidation of ore. A drilling rig was transported by helicopter to the borehole site in July 2006. A short casing was set and a rotary drill was used to expand the diameter (about 5 cm) and remove ice from a previously drilled borehole. After reaching the bottom of the old borehole, water from a freshwater lake was heated to about 30°C and was circulated through the borehole for 5 days prior to the initiation of coring in order to flush-out drilling brine and warm the rock surrounding the borehole. The sampling team (Pfiffner, Onstott, Ruskeeniemi, Johnson, and Tallika) arrived and set up a temporary core processing lab.

A 1% perfluorocarbon tracer solution was added to the drill water. The tracer solution was pumped into the drill water during the entire coring operation in order to evaluate whether or not any mixing of the drill water with saline groundwater was occurring. Samples of drill water were collected during each core run. Cores for microbial analyses were collected every 7th core run for a total of 10 cores. Immediately prior to a microbial core run, core liners were sterilized with methanol and inserted into a separate wire-line core tube. A small plastic bag containing 5 milliliters of fluorescent microspheres (109 spheres/milliliter) was inserted into the core catcher at the bottom of the core tube. Temperature monitoring strips were inserted between the core liner and the core barrel to measure the maximum temperature experienced by the core run.

When the coring run was completed and the wire line core barrel brought to the surface, the core liner and core were pushed from the coring tube, cut into 30-inch sections and placed into the cooler with ice packs. The cooler was filled with argon gas to keep the core as anaerobic as possible and the cooler was carried by hand to the core processing lab. Core sections in core liners were transferred into the glove bag and onto sterile paper. The core liner was removed, the core segments photographed and logged, and the core segments broken with sterile a hammer and placed into separate plastic sample bags.

The rate of penetration averaged ~30 meters per day with a 24 hour operation. The temperature strips were used to monitor temperature in the core barrel, but these proved inaccurate as their temperature quickly equilibrated with air temperature upon removal from the core barrel. Nevertheless they seemed to record increasing temperature with depth. Coring continued for 7 days until obtaining a down-hole depth of 535 meters (200 meters of core) at which point various lines of evidence indicated that the drill was below the base of the permafrost. At that point a temperature probe was lowered down the drill string to estimate the temperature at the bottom of the hole (it read 7-8°C). The drill string was quickly removed before it froze in place, casing was inserted into the borehole to a depth of 320 meter to maintain stability in the permafrost region and to keep the ice from melting and sealing the hole at that point. The drilling water was then removed using an 18 L volume bailer that was dropped down the hole and raised 19 times during a 12 hour shift. The temperature of the water was ~2.8°C. The conductivity of the bailed water varied from 1.8 to 4.10 millisiemens/cm. Throughout the next day, four additional bailer samples were taken. The conductivity increased to 7.96 millisiemens/cm or about 6,000 parts per million of total dissolved solids, which is more than 100-fold higher than the lake water used for the flushing water. In total about 400 L of water was removed from the hole in order to lower the water table into unfrozen conditions and to remove contaminating drilling water. During the process the borehole water cleared up and the increasing trend in salinity proved that the amount of formation water was continuously increasing in the mixture. The top of the water was determined by a down hole conductivity measurement to be at 492 meters (31th July) and an initial estimate of the influx rate was about 1 L/hour The borehole iced closed at a depth of 125 meters capturing the down-hole probe in the process. An attempt to drill out the ice without using hot water failed. Further attempts at sampling during the 2006 field season ceased at that point.

An initial 35S-sulfate autoradiographic survey of the cores returned from High Lake after last summer’s coring campaign has been completed. The survey quantifies the rate of microbial sulfate reduction after 3 months at 4°C. This survey also reveals the spatial distribution of sulfate reducing activity and indicates that some cores may be contaminated, but most are not. Some cores fail to reveal any significant microbial sulfate reduction compared to negative controls. The estimated rates are consistent with what has been reported for deep sea sediment, however the porosity of the rock cores are far less than that of deep sea sediments, which is perplexing. Samples of the 35S-sulfate autoradiographic rock surfaces have been preserved for Fluorescence In Situ Hybridization-Catalyzed Reporter Deposition (FISH-CARD) imaging. The last several months have focused on extraction and amplification of deoxyribonucleic acid (DNA). To date this has failed due to some dissolved substance that is apparently inhibiting the Polymerase Chain Reaction and Multiple-strand Displacement Amplification (MDA) reaction as revealed by positive spikes of the core prior to crushing. A more sophisticated approach for separating the DNA from other contaminants in the extract is being developed.

The High Lake deposit was originally discovered in the 1950’s by recognition of kilometer-scale gossans which result from reaction with natural acidic solutions during surficial oxidation of the ore. The gossans are readily visible in satellite images by their reddish-orange color and complete lack of vegetation. Drilling indicates that the gossan development only penetrates about 1 meter into the bedrock, stopping at the top of the permafrost. This indicates that the intensive rock weathering process has taken place since deglaciation within the last few thousand years. Elemental analyses coupled to scanning electron microscopy and X-ray diffractrometry reveal a broad range of geochemical environments. These petrographic studies suggest that dehydration was accompanied by an increase in acidity and sulfate concentration causing the weathered ore to move from goethite stability field into jarosite stability field with the precipitation of gypsum as dehydration product. The gossan was typified by a lack of diverse sulfate species and smaller crystal size compared to acid mine drainage sites like Rio Tinto and Iron Mountain. Phosphate minerals, however, were more prevalent than have been reported (so far) from these two sites. It does appear that the Martian mineral suites observed at Merridiani by Opportunity can occur on Earth in an arctic gossan environment. Mossbaur analyses of High Lake core samples by Dick Morris of Johnson Space Center has confirmed the presence of jarosite, hemtatite, subparamagentic goethite and nanophase Fe oxide.