A hypothesis for the geochemical anomaly in the North Creek Watershed /

A regional geochemical reconnaissance by bottom stream sediment sampling, has delineated an area of high metal content in the north central sector of the North Creek Watershed. Development of a geochemical model, relating to the relative chemical concentrations derived from the chemical analyses of bottom sediments, suspended sediments, stream waters and well waters collected from the north central sector, was designed to discover the source of the anomaly. Samples of each type of material were analysed by the A.R.L. Direct Reading Multi-element Emission Spectrograph Q.A. 137 for elements: Na, K, Ca, Sr, Si, As, Pb, Zn, Cd, Ni, Ti, Ag, Mo, Be, Fe, AI, Mn, Cu, Cr, P and Y. Anomalous results led to the discovery of a spring, the waters of which carried high concentrations of Zn, Cd, Pb, As, Ni, Ti, Ag, Sr and Si. In addition, the spring waters had high concentrations of Na, Ca, Mg, 504 , alkalinity, N03' and low concentrations of K, Cl and NH3. Increased specific conductivity (up to 2500 ~mho/cm.) was noted in the spring waters as well as increased calculated total dissolved solids (up to 2047 mg/l) and increased ionic strength (up to 0.06). On the other hand, decreases were noted in water temperature (8°C), pH (pH 7.2) and Eh (+.154 volts). Piezometer nests were installed in the anomalous north central sector of the watershed. In accordance with the slope of the piezometric surface from wells cased down to the till/bedrock interface, groundwater flow is directed from the recharge area (northwest of the anomaly) towards the artesian spring via the highly fractured dolostone aquifer of the Upper Eramosa Member. The bedrock aquifer is confined by the overlying Halton till and the underlying Lower Eramosa Member (Vinemount Shale). The oxidation of sphalerite and galena and the dissolution of gypsum, celestite, calcite, and dolomite within the Eramosa Member, contributed its highly, dissolved constituents to the circulating groundwaters, the age of which is greater than 20 years as determined by tritium dating. Groundwater is assumed to flow along the Vinemount Shale and discharge as an artesian spring where the shale unit becomes discontinuous. The anomaly is located on a topographic low where bedrock is close to the surface. Thermodynamic evaluation of the major ion speciation from the anomalous spring and surface waters, showed gypsum to be supersaturated in these spring waters. Downstream from the spring, the loss of carbon dioxide from the spring waters resulted in the supersaturation with respect to calcite, aragonite, magnesite and dolomite. This corresponded with increases in Eh (+.304 volts) and pH (pH 8.5) in the anomalous surface waters. In conclusion, the interaction of groundwaters within the highly, mineralized carbonate source (Eramosa Member) resulted in the characteristic Ca*Mg*HC03*S04 spring water at the anomalous site, which appeared to be the principle effect upon controlling the anomalous surface water chemistry.

HG 186.9-187.0 D.E-3

Fractured and weathered grains throughout the section. Lineations and grain stacks throughout the section.

HG 187.45-187.65 Thin Section

Coarse grained sediment with fine grained domains throughout. The clasts in the coarse grained domain range from sub-angular to sub-rounded. Short distance lineations are present throughout the sample. Organic rich domains (darker) are prevalent alongside fractured grains.

HG 225.15-225.25 Thin Section

Dark brown sediment with sub-angular to sub-rounded grains, that range from small to medium in size. Lineations with fractured grains are abundant, and grain crushing can also be seen. Minor rotation can also be seen.

HG 244.40-244.50-A Thin Section

Dark brown sediment with sub-angular to sub-rounded clasts. Rotation structures and lineations are common. Clasts ranging from small to large in size. Many large grains are fractured. Minor amounts of grain stacking and crushing can be seen. A few clay and organic rich domains can be seen.

HG 264.30-264.45

Coarse grained sample with clasts that range from small to large in size. The clast shape ranges from angular to rounded, and many grains are fractured. Grain crushing is present in large amounts. This includes edge-to-edge crushing as well as grains that are crushed into one another. Rotation structures are also common among the clasts that are sub-rounded to rounded. Areas of finer sediment can also be seen.

HG 276.80-276.95 Thin Section

Coarse grained sample, with grains ranging from small to large in size. Shapes range from angular to rounded. This sample is abundant in lineations, and rotation structures can also be seen around larger aggregates. Many large grains are fractured and minor grain stacking can also be seen.

HG 427.45-427.55

Brown sediment with grains ranging from small to large. The clast shape of this sample ranges from sub-angular to sub-rounded. Grain crushing can be seen in large amounts, and commonly involves the larger grains. Many of the larger grains are also fractured. Lineations and comet structures can also be seen.

HG 437.50-437.55

Light brown sample with clasts ranging from small to large. The clast shape ranges from sub-angular to sub-rounded. Grain crushing is common in this sample and mainly involves the larger clasts. Many grains are also crushed into one another. The larger grains are also fractured. Lineations and faint water escape structures can also be seen. This sample also contains a finer grained domain, darker in colour.

HG 493.80-493.90

Coarse brown sediment, with clasts ranging from small to large in size. Clast shape ranges from sub-angular to rounded. Lineations and grain crushing are common throughout the sample. It also contains comet structures and a few rotation structures. Many of the larger clasts are also fractured.

HG 3.75-3.85

Dark brown sediment with clasts ranging from small to large. The clasts range from angular to sub-rounded in shape. The sample mainly contains edge-to-edge grain crushing and rotation structures. Many grains are fractured and a few necking structures can also be seen.

HG 18.50-18.55

This sample contains grains that range from small to large in size. The clast shape ranges from angular to rounded. Many grains are fractured and grain crushing is commonly seen. A few necking structures and rotation structures can also be seen.

HG 28.75-28.90

This sample contains clasts that range from small to large. A few fractured grains can be seen. The grain shape ranges from angular to rounded. Rotation structures can be seen throughout the sample along with some edge-to-edge grain crushing.

HG 64.80-64.90

Dark brown sediment with clasts ranging from small to large in size. The clast shape ranges from angular to sub-rounded. Many of the larger clasts are fractured. Grain crushing is abundant throughout the sample. A few lineations can also be seen throughout the sample.

HG 168.50-168.60

Brown sediment with three main domains; two different fine grained domains and one coarse grained domain. The fine grained domains can be distinguished based on the abundance of organic material (darker). Both domains contain lineations. The coarse grained domain contains clasts ranging from small to medium in size and angular to rounded in shape. Rotation structures, lineations and comet structures can be seen in this domain. It also contains some fractured grains.