Lakehead University Geology - Journal Yearbook (Thunder Bay, Ontario Canada)

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Besides the rhombopyre dykes mentioned above, there are several dykes cutting the complex. At stop 3 two vertical dykes cut the syenite. These and the one at stop 7 were diabasic and might be related to the Keeweenawan extrusives in Central Canada. Also at stop 8 there were several series of high angle dykes of olivine-basalt in various host rocks. These and other structures, such as the sill of basalt at stop 6 might be the equivalent of Animekie extrusives, but further study is necessary to substantiate this. One way to do this is by radiometric dating and the initial 87Sn 86Sn ratio which should be the same for all co-magmatic rocks. These and other studies might reveal the relationship of these structures to the other regional phenomena, such as the dykes which might be feeders to the regional Keeweenawan extrusives. The rocks in the complex itself are very interesting and spectacular in their variety, texture, rare minerals and elements, and in the sequence of crystallization. Economically the potential of nephelene syenite and laurvakite for construction material, and the other rare elements might be worth investigating. Further study may contribute to the understanding of pre-Cambrian strati- graphy in the Canadian Shield or even in the crust. Subsequent Field Trips 1 . Sibley Penninsuia field trip 2. Kakabeka Falls - Armstrong field trip 3. Shebandowan field trip 4. ShebandDwan undei ground field trip 60

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In several outcrops we saw xenoiiths of different sizes and composition, mainly basalt. For ex- ample, at stop 2, just off the highway, was a large xenolith of basalt, and at stops 3 and 4 there were xenoiiths of basalt and breccia in the syenite. Most of them showed evidence of slow sinking. F. Puskas suggested that these were from the Coubran Lake volcanic cap and that the intrusion was a lopolith where the present level of exposure is near roof. The consistent fracture and shear zones might also expose some interesting structures. For instance, at stop 4 there was a domelike structure with pre-Coldwell rock sheared and fractured on top of the Coldwell gabbro. Also, at stop 9 near the western margin of the complex, there were two main directions of fracture - one vertical and one horizontal in the south-east direction. The rocks in the complex show complicated structural and age relationships as well as diversified composition. The oldest was the gabbro, followed by laurvakite, syenite and related rocks. But at stop 4, within a few feet the gabbro changed in composition from common to leucocratic gabbro due to an increase in acidic content. This change might be due to the interaction of syenite with gabbro (hybridi sation). The laurvakite also shows variations in composition - at stop 1 it was much altered, with plenty of quartz, calcite and pegmatite veins. The laurvakite is also rich in olivine in molybdenite, and native Mo., but in areas such as stop 8 it is very fresh and approaches the composition of a syenite. Most impressive of all are the variations in the syenite. In stops 2 and 8, the feldspars are very pinkish, probably rich in hematite due to alteration. At stop 2 it was intruded by the rhombopyre dyke near the Bamoos Radio Station, implying an older age relative to the rhombopyre dyke. At these stops, the syenite shows an intersertal texture of the potassium feldspars in a matrix of mainly mafic minerals, with evidence of agpaiitic sequence of crystallization. The syenite is much altered whereas the rhombopyre is rather fresh. At stop 4 we actually saw some xenoiiths of syenite in the gabbro, but at stop 5 the nephelene was very prevalent in the syenite, which is rather fresh with alteration only of nephelene to zeolite. Finally at stop 5 » on our way down the railway road near Port Coldwell, we saw the fresh nephelene syenite dying out into the altered, pinkish normal type of syenite - and yet at stop 7 two series of syenite veins cut each other, in diabase. These observations imply that the intrusion is not as simple as F. Puskas has anticipated. It can only be explained by the occur- rence of multi-stage crystallization and local variation in the order of crystallization. Generally, the main part of gabbro crystallized out first, then the normal syenite which became altered either before or during the intrusion of the rhombopyre dyke, followed by the intrusion of the syenite by the dyke. A second and significant portion of syenite rich in nephelene crystallized out, breaking up some older syenite and the rhombopyre dyke. Somewhere another, but insignificant, portion of gabbro crystallized out and engulfed some of the older syenite. The laurvakite generally fits into the pattern after the crystallization of the first portion of gabbro, but another part might have formed later - or the change in composition and amount of alteration can be attributed to local magmatic differentiation and environment alone. Ae seen at stops 1 and 5» the pegmatites and others in various rock types were always of late origin. They usually occurred in veinlets of the parent rocks and showed similar mineralogy, but their grain size and composition altered relative to the distance from contact. For example, the pegmatite at stop 6 can be attributed to the late magmatic portion of magma rich in volatiles, crystallized in fractures in the already solid rock. Since the whole complex is generally rich in rare minerals and elements, it might be interesting to do a chemical analysis of these pegmatites. There are also some features of geochemical interest, one being the agpaiitic sequence of crystal- lization in the altered intersertal syenite. Another is the interaction among various rock types evident in the xenoiiths and surrounding rocks, and the contact between various veins. To mention a few, the xenoiiths of gabbro in syenite (stop 7)» remained fresh and retained sharp boundaries; the rhombopyres and breccia at the same stop showed similar features. But several hundred feet away, the two series of syenite veins in the so-called nephelene syenite veins showed where they cross-cut each other in a complete fusion of their contact. This can be explained by the similarities and differences in the composition of the host and foreign material. When syenite veins meet and cut each other, it is not hard chemically for solution and recrystallization near the contact, whereas the reaction between a gabbro and a syenite is much more difficult, if not impossible. The alteration in nephelene syenite to colourful zeolite might be worth studying too. Mineralization occurred in several places. Common ores such as pyrrhotite, pyrite, chalcopyrite and iron oxides were seen in many outcrops in small amounts. But at stop 1 the molybdenite associated with laurvakite is rather rare. Further study might reveal yet other interesting elements and minerals such as titanium. At stop 8 large amounts of magnetite were seen either in nearly pure forms or injected into the surrounding rocks such as syenite and gabbro. 59

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The LongView (Home, photographed from 22,000 miles away) Most of us at Texas Gulf have children. Many, including the president, have young children. These are a multitude of reasons why the long view of the world is a way of life at Texas Gulf Sulphur Company. Even without the children, a company which has been successful in developing natural resources over several generations would emphasize long-range planning, thinking in terms not just of five or ten years ahead, but 20, 50 and 100 years. A major mine with its processing and related facilities must be viable for at least two decades rf it is to be rewarding to stockholders, employees and the community. Executives of natural resources companies learn to contemplate the prospects for developing natural resources for their children and children’s children; the materials for continued growth in the devel- oped regions of the earth; the requirements for eradicating poverty, disease and starvation in less privileged parts of the globe and the wherewithal for setting them on the way to fuller development. They must think of how these things may be done without disturbing man’s environ- ment in unacceptable ways. The long view is a way of life for us. Texas Gulf Sulphur Company.