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Lake Sediment Sampling Program Helps Detect
Mineral Potential

By Virginia Heffernan

Teams of provincial geoscientists are fanning out across Canada this summer for a fresh season of mapping and sampling that should detect undiscovered areas of mineral potential. And create a whole lot of new data.

One of the main projects within the sedimentary geoscience section of the Ontario Geological Survey (OGS), for instance, is a multi-year lake sediment sampling program that is building a geochemical picture of northern Ontario.

Under the program, the OGS has been collecting tens of thousands of samples from the more than 250,000 lakes that dot Ontario in order to support mineral exploration and provide high-quality baseline geochemical data.

Over the past 20 years, the high-density sampling (about one sample per 3 km2) has covered about a third of the province. OGS geochemist Richard Dyer estimates he will collect about 2,000 lake sediment samples over an area of 6,000 square kilometers this summer alone.

The resulting dataset is becoming so large that using conventional tools to display the information can be painstakingly slow.

As a result, the OGS has created an add-on to Google Earth called OGS Earth that allows even novice users to integrate multiple geological data layers such as lake sediment sample results, geology, topography and cultural information in virtual 3-D, quickly and easily.

But for more sophisticated interpretation, the OGS will use Geosoft's recently released Geochemistry for ArcGIS extension to analyze the lake sediment data within a GIS environment.

The new extension allows geoscientists to examine multivariate relationships, uncover underlying structures, identify outliers and anomalies, and present results on maps that are both visually striking and informative.

The software contributes to a smooth workflow - from importing the data, through to quality control, analysis, and integration of other datasets and finally to visualization in a way that is meaningful to colleagues, managers and mining companies.

"We're able to take the data from the lab with very minor manipulation, extract the standards, plot it up and immediately start working with data using one program," says Dyer. "Before, we had to bring the data into (Microsoft) Excel, massage it, then bring it into (Microsoft) Access, run some queries, spit the data out again and bring it back into Excel. If there was any problem along the way, you'd have to go back to square one."

Dyer sees the extension proving useful for the OGS's other regional geochemical sampling programs, including an ongoing groundwater sampling project in southern Ontario.

Geoscientists at the Manitoba Geological Survey are equally eager to try out the geochemistry extension on their new sampling initiative in the Flin Flon greenstone belt. Working in collaboration with Ryan Morelli at the Saskatchewan Northern Geological Survey, Manitoba's Renée-Luce Simard will look under the Paleozoic cover rocks to find new VMS deposit potential in the prolific base metal-rich belt that straddles the provincial border.

The Flin Flon and Snow Lake districts host numerous world-class VMS deposits, including four operating mines (Callinan, Triple 7, Trout Lake, and Chisel North), many past-producing mines, and several unexploited deposits, including the newly-discovered Lalor deposit. All of them are located in the portion of the belt where the Precambrian host rocks are exposed.

To the south, the host rocks dive under up to 300 metres of Paleozoic limestone, making exploration more challenging. Still, both the provincial surveys and mining companies working in the area believe it is only a matter of time and technology before equally rich deposits are found beneath the cover rocks. 

Geophysics and follow-up drilling are the traditional methods used for finding buried deposits, but subsurface geochemistry also has a story to tell. Simard will be investigating the geochemistry of existing drill holes in order to piece together a map of the subsurface that – in combination with the geology and geophysics - will serve as a guide to further drilling.

The project is funded in part by the GSC's Targeted Geoscience Initiative (TGI) designed to lead to new discoveries in established mining communities. It stretches from the Flin-Flon Creighton area on the Manitoba-Saskatchewan border to Lynn Lake further north and involves targeted bedrock and surficial mapping, airborne geophysics, seismic exploration and geochemistry.

Simard's team is involved in the third phase of the project, designed to develop methods to detect geochemical signatures of the buried VMS deposits.
 
"There is a lot data and that's where the Geosoft extension will be fantastic," says Simard. "There are over three thousand drill holes in the sub-Phanerozoic. The companies have been sharing the geochemistry for these drill holes with us, so at up to twenty-five samples per hole, that's a lot of data to sort through."

Because the holes are widely distributed over hundreds of kilometres and there is no exposure at surface, it can be difficult to pinpoint sample locations. This is where Simard sees the geochemistry extension being especially useful.

"There is software out there that allows us to display the geochemistry on an x-y scatterplot or triangular plot to get the geochemical signature of the sample, but you don't know which sample has which signature because there is no link to your map" says Simard. "With the Geosoft software, when we select samples on the scatter diagram they are automatically highlighted on the map. That's a powerful tool."

 Simard will be using the geochemistry extension in combination with Target for ArcGIS in order to come up with a 3-D interpretation of the subsurface and even produce new geological models for areas that have higher-density drilling. And as the baby boomer generation of government geologists retires, Simard sees a need for preserving the old data and making it relevant to incoming geologists.

"We have a lot of legacy issues in the sense that people that are retiring have huge datasets and knowledge of an area that need to be passed on." she says.  "The traditional solution would be to find the geochemistry database, go back to the notes, go back to the map and then plot each and every sample. The geochemistry extension does 95% of this work for us. You can make an association between the geochemical signature and the map, even if you've never been there or weren't the one who collected the samples."

Government surveys at both the national and regional level are becoming guardians of an increasing amount of data that needs to be readily accessible and easily displayed by industry and other stakeholders. Innovations in software and technology are helping them to provide that level of service.