The distribution of cobalt and nickel in some sulphide deposits of the Flin Flon Area, Saskatchewan
Faulkner, Edward Leslie
The purpose of this section is to outline the general development of this study, and to indicate why certain investigations were carried out, and why others which might appear to have equal merit were discarded. In 1959, the Geology Department of the University of Saskatchewan, in conjunction with the Geology Division of the Saskatchewan Research Council, decided to co-ordinate a number of research projects and some future field work in one general area, and selected the Flin Flon area for this purpose. Apart from being readily accessible, work which had already been carried out in the area, notably the mapping of the area surrounding Amisk Lake, Saskatchewan, to the west of Flin Flon by Dr. A. R. Byers, (Byers and Dahlstrom, 1954, Byers and Kirkland, 1964), had indicated a variety of interesting problems which deserved further study. One of these was the genesis of a number of base metal sulphide deposits. These deposits seem to fall into two groups. There are a large number of deposits which consist almost entirely of pyrrhotite or pyrite, or mixtures of the two, with nominal amounts of other base metal sulphides. For convenience these will be referred to as the 'barren' deposits. Then there are a much smaller number of deposits which consist of pyrrhotite or pyrite or mixtures of the two, with much larger quantities of other base metal sulphides, particularly chalcopyrite and sphalerite. These deposits, which may or may not be of commercial value, will be referred to as the 'economic' deposits, and include the main Flin Flon ore body, and a number of other mines, past and present such as the Coronation and Birch Lake Mines. Apart from this major difference in quantitative mineralogy the structural and geological setting of both groups is quite similar in many respects. A better understanding of the genesis of these sulphides could have considerable practical value in the search for new 'economic' deposits, quite apart from any purely theoretical value. The original purpose of this thesis was to make a study of the genesis of these sulphide deposits, with emphasis on a general geochemical approach, to see if there were in fact, other basic differences between the two groups of sulphide deposits, apart from the obvious difference in quantitative mineralogy. This aim was greatly facilitated when the National Advisory Committee on Research in the Geological Sciences chose Coronation Mine, some fourteen miles southwest of Flin Flon, as the site of a co-ordinated research program to be conducted by any interested bodies, under the general guidance of the Geological Survey of Canada, who in turn assigned Dr. D. R. E. Whitmore to the task of co-ordinating the various investigations. It was thus possible to make a detailed collection of samples from Coronation Mine, as a representative of the 'economic' group, during the summer of 1960, and on subsequent occasions as mining progressed, as well as to do underground structural mapping as a contribution to the Coronation Mine Project. This latter also provided a very necessary background for the geochemical work. Samples from the 'barrenâ€¢ deposits were represented chiefly by material previously recovered from exploratory drill core and surface workings by Dr. A. R. Byers, together with a few samples I was able to salvage myself. Unfortunately this record is far from complete, as much of the drill core from a number of prospects has been disposed of, or is otherwise irrecoverable. The geochemical work of this thesis resolved itself to some extent, in that the equipment available limited analytical work to chemicalspectrophotometric and flame-photometric methods. Due to the inherently poor productivity of chemical procedures, especially where geological samples are involved, the geochemical work had to be restricted to a few studies to which there was the best chance of attaching some geological significance to the analytical results. Two possibilities appeared likely to provide the most useful information: whole-rock, and trace element studies of ore and altered wallrocks from Coronation Mine. trace element studies of pyrrhotite from both 'economic' and 'barren' deposits. Even so, considerable preliminary chemical work was necessary to adapt existing analytical procedures to give reliable results with the available equipment, and with the particular type of samples involved. The results ot preliminary whole-rock analyses and some trace element determinations on altered wallrocks were somewhat disappointing, in that the conclusions which could be drawn from the results were essentially negative. It was felt that a detailed study along these lines would be valuable, but that it would involve an experimental program beyond the scope of this thesis, and perhaps better suited to more rapid physical methods of whole-rock analysis. This work was therefore discontinued. Attention was then concentrated on trace element determinations of pyrrhotite from both 'economic' and 'barren' deposits. Apart from some preliminary work on other sulphides, pyrrhotite was chosen for study because it was common to both groups of deposits, and because it was the most widespread sulphide in the available sample collection. The trace elements selected for study were cobalt and nickel, because it would probably be easier to attach geological significance to the analytical results than might be the case with cadmium or lead data for example. This work in fact, revealed considerable differences between the two groups of sulphide deposits, and the description of these findings, and a consideration of their implications form the main portion of this thesis. Although this purely geochemical work could have stood on its own, the original intention of the thesis, that of using the geochemical data to throw light on the genesis of the sulphide deposits, has not been overlooked. A consideration of the new data in the light of the available field evidence shows that a theory for the formation of the 'barren' sulphide deposits can be proposed which is consistent with the available data. Difficulties are encountered in finding a satisfactory theory for the formation of the 'economic' deposits however. These difficulties chiefly concern the structure and age of the 'economic' mineralization in the Coronation Mine-Birch Lake area. Various genetic theories which have been proposed for these sulphide deposits by other workers or which might have some bearing in this particular study are briefly reviewed and are also found to be unsatisfactory or inadequate in one respect or another. It was felt that some of these difficulties might be resolved if partial remobilization of the sulphides had occurred and possible evidence in support of remobilization is briefly considered. The thesis therefore consists of three main sections. although there is necessarily some overlap of material dealt with in each section. There is a brief section on the geological setting and description of the sulphide deposits, after which follows the main section on the geochemistry, and the discussion of the results and the genesis of the sulphide deposits. These are followed by a brief conclusion and some suggestions for further studies. A number of appendices contain some additional details or information on various points which occur in the main text.