Meguma, the most outboard northern Appalachian terrane, is characterized by Upper Neoproterozoic to Lower Ordovician turbiditic rocks that have an exposed thickness of more than 11 km. As a result of geological mapping, combined with petrological studies, the stratigraphy of these rocks has been redefined. The traditional twofold division into the meta-sandstone–dominated Goldenville Group and the overlying slate-dominated Halifax Group is retained, but the Chebogue Point shear zone divides these groups into western and southern stratigraphic packages containing different formations. In both packages, psammitic rocks are dominantly feldspathic wacke, and they have mineralogical compositions indicative of deposition in an active margin from a source dominated by quartz and plagioclase; rare conglomeratic units contain mainly psammitic clasts with some mafic through felsic volcanic clasts, and rare tonalite clasts. In the southern area, psammitic units tend to contain more quartz and grade to arenite. Although fine material increases in relative abundance, little change in provenance up section is indicated by petrography of psammitic rocks. Chemical compositions of 116 psammitic and pelitic samples from the western area and 471 from the larger southern area are consistent with the petrographic data. Their compositions are indicative of derivation from felsic to intermediate igneous material, and the depositional environment was probably in a rift along the Gond wanan margin. It is likely that Pan-African orogenic belts containing recycled sediments from older cratons were major contributors to the sediments, rather than sediments being derived directly from large ancient cratonic areas.

The East Kemptville greisen-hosted tin deposit (58 million tonnes of 0.165 percent Sn), southwestern Nova Scotia, Canada, occurs beneath undulations in the contact between granitic rocks of the Davis Lake complex (DLC) and Meguma Group metawacke. Cassiterite-topaz ore precipitated from a F- and Sn-rich fluid derived from the East Kemptville leucomonzogranite. Controls on tin mineralization include the unusual primary Sn and F abundances of the DLC magma, the vertical chemical zonation of the magma prior to crystallization, generation of an aqueous phase, and associated Sn-Cl complexing before the separation of F from the magma and the flat-lying granite-metawacke contact. The Carboniferous DLC is composed of biotite-bearing monzogranites, leucomonzogranite, and high-F, low-B topaz greisen. The chemical and isotopic signatures of the monzogranites reflect the unusual source of this highly evolved pluton. Magmatic evolution was focused toward the granite-metawacke contact and culminated, at the current erosional level, in the East Kemptville deposit. Chemical variation is attributed to the vertical zonation of the magma prior to the fractionation of biotite, K-feldspar, ilmenite, and REE-bearing phosphate minerals. The remarkably high F and P contents resulted in unusual Al and P distributions and concentration of metals beneath the contact as a result of increased magmatic depolymerization and diffusion. Pegmatitic segregations record the evolution of a F- and Sn-rich aqueous fluid. This aqueous phase scavenged Cl, alkali elements, P, Sn, and other metals from the magma, concentrating them beneath the contact. In contrast to porphyry-style deposits, this fluid was not expelled from the granite. When crystallization was complete, more than 10,000 tonnes of F partitioned into this aqueous fluid, forming a hydrofluoric fluid that was neutralized by reaction with the leucomonzogranite. Quartz-topaz rock is either a direct precipitate from the F-rich fluid or extensively replaced leucomonzogranite. Quartz-mica greisen and incomplete greisen formed as the F/OH ratio in the fluid decreased. Veins and fractures emanating from massive greisen zones have alteration envelopes, indicating these structures were conduits for the F-rich fluid. Their orthogonal orientation suggests these veins are related to cooling, not hydraulic fracturing. Whole-rock Rb-Sr isotopic data from leucomonzogranite and quartz-topaz rocks yield dates and initial ratios statistically identical to the biotite monzogranite. High mean square of weighted deviations (MSWDs) resulting from the former data reflect contamination of the late-magmatic fluids by Sr derived from the metawacke and later thermal overprinting. Deformation, probably related to regional tectonothermal events, affected all rocks of the DLC, but postdates ore formation.

Location Coast of Clare, between Yarmouth and Digby; centered on44°05'N Lat.; 66°10' W Long. (Fig. 1). A nearly continuous 48-mi (80-km) exposure reveals a Quaternary sequence that recordsthe major geological events of the last 130,000 years. Yarmouthcan be reached by air from Boston and Halifax. Ferriesconnect Yarmouth and Digby with Bar Harbour and Portland, Maine, and with Saint John, New Brunswick, respectively. Railservice and Nova Scotia 101 and 103 link Yarmouth and Digbywith Halifax. A network of roads gives access to each site. Accommodationis plentiful en route; car and bus rentals are availablein Yarmouth and Digby. All sites are reached by publicroads and by short walks along public beaches. No permission isrequired, except at Pembroke Cove. Additional maps: Nova Scotia Highway Map–free at entry points; Geological Highway Map and Pleistocene Geology Maps 7 and 8 may be orderedfrom the Nova Scotia Department of Mines, Box 1087, Halifax, B3J 2X1, Canada; and 1:50,000 topographic maps (21 A5 and12; 21 B 1 and 8) may be ordered from Canada Map Office, Ottawa, K1A 0E4. Taylor (1969) treats the bedrock geology;Goldthwait (1924) and Roland (1982) the physiography.