Transects produced by the North American Continent-Ocean Transect Program (Speed and others, 1982; U.S. Geodynamics Committee, 1989) describe the complex orogen formed along the Late Proterozoic to Early Cambrian rifted margin of the Laurentian craton, including continental rocks of the Grenville province, which themselves had been earlier formed by a Middle Proterozoic continent-continent collision. Continental accretion was followed by continental separation and the formation of a passive continental margin. This 900-km-long transect crosses the entire Appalachian orogen and the passive continental margin from the craton to Atlantic oceanic crust. It is supported by abundant seismic reflection and refraction data that were gathered specifically for this transect, in part, to resolve questions posed by the earlier transects across the Atlantic passive continental margin. Thus, it is a second-generation transect. This transect has been accepted in the Global Geoscience Transects Project (CC-7) of the InterUnion Commission on the Lithosphere, International Council of Scientific Unions (Monger, 1986) as Transect 8. The Quebec-Maine-Gulf of Maine transect provides excellent data that can be used to understand the processes of continental accretion and separation. An uncertain number, possibly ten or more, of tectonostratigraphic terranes of predominantly continental affinity were accreted to the craton, as shown by the transect. In addition, at least two oceanic terranes also were accreted. Although some terranes had been joined together to form composite terranes before being accreted (Boone and Boudette, 1989, describe an example), in general, these terranes were accreted episodically to the southeastern (current geographic direction) part of the craton by thrust and (or) strike-slip faulting at successively younger times during the Paleozoic. The terranes differ principally in the nature of their Late Proterozoic to middle Paleozoic history and stratigraphy (Keppie, 1989) and paleontology (Neuman and others, 1989). Accretion in the part of the orogen shown on this transect took place during multiple collisional or transpressive episodes in the early and middle Paleozoic. . A very thick continental crust was produced during these episodes. Geologic evidence that indicates the formation of this
Quartz-molybdenite veins up to 15 cm in width occur in fine to medium-grained porphyritic biotite-hornblende granodiorite at Priestly Lake north-central Maine. An area of about 150 m x 150 m contains quartz-molybdenite veins; a larger area is characterized by barren quartz veins. Quartz-molybdenite veins are concentrated within the most felsic variants of the intrusion as suggested by lower mafic mineral contents. The pluton has a narrow range in SiO2 (67-70 wt.%), major oxides, and in trace-element compositions. Molybdenite occurs as coarse grained clusters in pockets within the quartz veins, and fills fractures in the quartz veins and host rocks. Disseminated molybdenite in the granodiorite is relatively rare and occurs only in the area characterized by a high density of quartz veins (up to 50 veins per square meter). Alteration envelopes along the quartz veins are very thin or absent, although in some areas the granodiorite appears to be selectively and pervasively altered. Sericite, chlorite, epidote, calcite, pyrite, and quartz are concentrated near the quartz-molybdenite veins. Many of the field and geochemical characteristics of the Priestly Lake pluton are unlike those of major molybdenum-producing areas (Climax, Henderson, Urad). For example, the area of alteration seems to be of limited extent, the host rock is not intensely altered hydrothermally at the surface, the density of fractures is rather low in the mineralized area, and the amount of disseminated molybdenite appears to be small. However, the Priestly Lake pluton may be a small fraction of a concealed batholith as suggested by geophysical data. It is conceivable that the type of mineralization at the surface might be the expression of more extensive molybdenite mineralization at depth. The quartz-molybdenite veins in the Priestly Lake pluton are significant because they indicate that potential molybdenum sources for producing mineralized granites were available at depth. Future studies should be aimed at delineating the area of quartz-molybdenite mineralization, documenting hydrothermal alteration and zonation, determining fracture density, and evaluating the sulfide assemblage.
An 8-m-thick alkali-olivine basalt sill intrudes sediments that overlie oceanic tholeiitic flows. The average modal mineralogy is plagioclase (46.9% fresh, 5.1% zeolite and smectite replaced), clinopyroxene (23.8%), olivine (4.8% fresh, 6.0% smectite replaced), interstitial smectite (7.1%), titanomagnetite (3.4%), interstitial zeolite (2.4%), amphibole (0.3%), apatite (0.1%), chromian spinel (<0.1%), and sulfides (<0.1%). The cooling of the sill was slow enough to permit minor olivine settling but rapid enough to produce extreme compositional zoning in plagioclase and ferromagnesian minerals. Late-stage deuteric zeolitization was locally extensive. Development of an ophitic texture is related mainly to the relative position of clinopyroxene in the paragenetic sequence. Variation in Fe + Mg in plagioclase is sensitive to clinopyroxene crystallization. Clinopyroxenes are calcic aluminous augites showing an overall trend of Fe enrichment, with no Ca depletion, and a decrease in components other than Wo-En-Fs. Amphiboles (arfvedsonites, Ti arfvedsonites, ferrorichterites, ferroactinolites, and grunerites) crystallized as late-stage deuteric phases and are not the result of postcrystallization alteration. The paragenetic sequence is chromian spinel + olivine (Fo80-Fo65(?)) + plagioclase (An80-An65) → olivine (Fo65(?)-Fo15) + plagioclase (
The Mining and mineral processing industry is important to the Canadian economy and in 2001 contributed $35.1 billion, or 3.7 percent, to the Gross Domestic Product and employed approximately 376,000 Canadians (Minerals and Metals Sector, Natural Resources Canada). However, over the past decade, Canada's base metal reserves have declined by more than 25 percent, and significant new discoveries will be required if Canada's role as a major base metal producer is to be maintained into the twenty-first century. The Bathurst Mining Camp is one of Canada's most important base metal mining districts, accounting in 2001 for 30 percent of Canada's production of Zn, 53 percent of Pb, and 17 percent of Ag. In 1999, the Bathurst Mining Camp accounted for 32 percent of the Zn, 80 percent of the Pb, and 25 percent of the Ag reserves (Minerals and Metals Sector, Natural Resources Canada). The value of production from the Bathurst Mining Camp in 2001 exceeded $500 million and accounted for 70 percent of total mineral production in New Brunswick. Approximately 2,000 people are directly employed by the mining industry in the Bathurst Mining Camp. Without the discovery of new ore reserves, however, production will decline and will cease within about 10 yr at current production rates, and with it the principal source of economic activity in northeastern New Brunswick will also disappear.To address the major decline of mineral resources in Canada's economically important mining districts, EXTECH (Exploration and Technology) projects were established by the Geological Survey of Canada. EXTECH-II is a multidisciplinary, integrated and collaborative project that has focused on the Bathurst Mining Camp with four principal objectives: (1) update and expand the geoscience knowledge base, (2) develop and test new and improved methods of exploring for massive sulfide deposits, (3) conduct ground and airborne, geophysical and geochemical surveys to identify new exploration targets, and (4) build a multiparameter, comprehensive, coregistered, and internally consistent digital geoscience database of the entire Camp. Although EXTECH-II was initiated by the Geological Survey of Canada in 1994, it was a collaborative project involving earth scientists from the Geological Survey of Canada, the Department of Natural Resources and Energy of New Brunswick, universities, and mining and exploration companies.A similar multidisciplinary project was established at about the same time by the U.S. Geological Survey to study the well-preserved Bald Mountain Cu-Zn-Ag-Au massive sulfide deposit in northern Maine. This project, which began in 1995 and ended in 1999, also included selected research on the Mount Chase Zn-Pb-Cu-Ag-Au deposit 70 km to the south of Bald Mountain.
Lead isotope compositions of soils and near-surface tills from an area of coastal Maine known to have groundwater with anomalously high arsenic contents were measured in order to determine the source of the lead and, by inference, possible sources of arsenic. Five soil and till sites were selected for detailed chemical and isotopic analysis. To construct profiles of the soil and till horizons, five samples were collected at 10-cm intervals from the surface to the base of each horizon. Total lead and arsenic concentrations and lead isotopic compositions were measured for 48 leaches and bulk residues. The soils and tills are underlain by sulfidic schists of the Penobscot Formation. Several generations of minerals containing arsenic and lead exist in the regional bedrock, including rock-forming silicates (feldspar and micas), sulfide minerals formed during diagenesis (for example, arsenic-rich pyrite), and sulfide and oxide minerals that formed as a result of Silurian metamorphic and igneous events (for example, arsenopyrite, galena, iron-oxides, and arsenic-sulfides). A young group of secondary minerals (for example, iron-hydroxides, arsenic-hydroxides, lead-sulfate, and arsenic-jarosite) formed from recent weathering and pedogenic processes.
