Cargill Township carbonatite complex, District of ... - Geology Ontario

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CARBONATITE - ALKALIC ROCK COMPLEXES: CARGILL TOWNSHIP hedral twin planes. Allen (1972, p. 108, p. 105) reported that dolomite is ubiqui tous and rarely displays exsolution textures. Twyman (1983, p.95) interpreted the calcite morphology as secondary pro duced by brecciation. The carbonates contain minor Mg, Fe, Mn, and Sr; car bonates from the nearby Argor carbonatite contain more Fe (Twyman 1983, p. 122). The minor elements in calcite are inconsistent with chemical trends es tablished in other mineral phases, however in dolomite Fe enrichment trends are consistent with those found in amphibole and biotite (Twyman 1983, p. 122). Twyman (1983, p. 125) suggested this inconsistency possibly resulted from exsolu tion, recrystallization, and exchange of components between liquid and vapor. Twyman (1983, p.95) reported rare exsolved dolomite lamellae in the calcite. Apatite is present in all thin sections. The mineral occurs as rounded bead- like grains or rounded elongated grains. The mineral varies from anhedral to euhedral in form. Data obtained by Twyman (1983, p.218) indicate that apatite is a major car rier of rare earth elements (REE). The heavy rare earth element (HREE) con centrations are relatively constant throughout differentiation and the light rare earth elements (LREE) vary only slightly (Twyman 1983, p.219, 233). Twyman concluded that since the REE are not incompatible elements in a carbonatite magma they are not sensitive indicators of magmatic trends. Twyman (1983, p.224) suggested that whole-rock chemical compositions may reflect original magma (REE) compositions. Sharpe (1987) proposed that low rare earth contents in the rauhaugites may reflect lower apatite contents. Olivine forms anhedral to crudely euhedral grains*. The olivine in the core occurs as brown, resinous, glomeroporphyritic clots up to 4 cm in diameter within the carbonate. The mineral is generally fresh but commonly displays alteration along grain boundaries and fractures to yellowish clinohumite. The olivine is rarely serpentinized. Allen (1972, p. 125) reported a fosterite content of 81 to 82 mole percent for olivine from the carbonatite phase of the complex. Olivine poikilitically encloses apatite and amphibole. Twyman (1983, p. 135) described the olivines as MgO-rich, low in NiO and with moderate to high MnO content. Microprobe analyses showed the forsterite content to be 81 to S29& (Twyman 1983, p. 135). Based on olivine chemical com positions, Twyman (1983, p.200) suggested that the carbonatites were generated from mafic source material. Pyrrhotite occurs as anhedral disseminated grains and is widespread in occur rence. Amphibole occurs as pleochroic colourless to pale green, acicular grains. The grains are euhedral in outline and commonly display twinning. The amphibole may occur poikilitically within the olivine. In one instance the amphibole crystals appeared to occur as clots within the thin section. Allen (1972, p. 105) reported that the amphibole is a richterite or ferri-richterite and is commonly zoned. Gasparrini e t al. (1971) reported that amphiboles from the carbonatite display an increase of calcium, magnesium, and potassium towards the core of the grain and that iron and sodium increase towards the edge. Twyman (1983, p.96) indicated that the amphibole in olivine sovite is rich terite and within his arfvedsonite sovite the amphiboles are zoned from richterite 'The identification of olivine was confirmed by X-ray diffraction techniques by C. Peat, Royal Ontario Museum. 16
R. P. SAGE cores to magnesio-arfvedsonite rims. The amphibole composition is richer in Fe and alkalies and poorer in Ca and Mg as differentiation proceeds (Twyman 1983, p. 103). Twyman (1983, p. 100) reported little or no Mn, Ti, and Al in the amphiboles. At Cargill the K content of the amphiboles was observed to increase with differentiation (Twyman 1983, p. 146). Allen (1972, p.105) reported rare zircon, diopside, and ankerite in this rock unit. Rare zircon and very rare pyrochlore were reported by Twyman (1983, p.97, 140). Probe analysis of this rare pyrochlore indicates Ta, U, and light rare earth elements increase and Nb and Ca decrease from core to rim (Twyman 1983, p. 143). Twyman (1983, p. 143) correlated the pyrochlore at Cargill with the early formed pyrochlore found at the nearby Argor carbonatite. Sharpe (1987) completed microprobe analyses on both the carbonate and mafic silicate phases. Microprobe analysis of one sample from International Min erals and Chemical Corporation Limited diamond drill hole 23, drilled in the centre of the southern complex indicated the presence of vesuvianite (Sharpe 1987, p.27). This is the first known occurrence of vesuvianite within a car bonatite of which the author is aware. Sharpe (1987, p.26, 27, 32, 37, 38, 43, 44, 54) presented in tabular form considerable microprobe and chemical data on the Cargill carbonatite to which the reader may wish to refer. Silicocarbonatite With increasing accessory mineral content, sovite grades into Silicocarbonatite. In thin section the Silicocarbonatite is fine to medium grained, equigranular, hypid iomorphic to allotriomorphic, with straight to curved grain boundaries. An estimate of the mode is 5 to 5596 phlogopite, l to 3096 magnetite, O to 1096 clinohumite, 15 to 5096 carbonate, O to 596 apatite, O to 3096 olivine, and 2 to 7096 amphibole. Phlogopite forms anhedral to subhedral grains, and commonly displays a darker reddish brown rim similar to that observed in the sovite. Some grains display kinking or bending of the (001) cleavage. Magnetite forms anhedral to subhedral grains. The magnetite occurs as dis seminated grains and also as granular aggregates. Clinohumite occurs as anhedral grains along fractures within, and along grain boundaries of olivine. The clinohumite has a distinctive yellow color in thin sec tion. Carbonate grains form an anhedral interlocking mosaic. Twin planes on the carbonate grains may be bent in those samples displaying cataclastic textures. Apatite occurs as rounded bead-like grains and as rounded elongated grains. Olivine occurs as anhedral to crudely euhedral grains. Trace to minor serpen tine may also be present. Amphibole occurs as acicular crystals with a pale green color. Slight changes in birefringence between core and rims of some grains suggests that the amphi bole may, at least locally, be compositionally zoned. Rauhaugite Within the central zone of the complex, dolomite becomes the most abundant carbonate phase. The presence of dolomite was confirmed by X-ray diffraction by W. Hicks, Geoscience Laboratories, Ontario Geological Survey. The 17
Page 1 and 2: THESE TERMS GOVERN YOUR USE OF THIS
Page 3 and 4: Ontario Geology of Ministry of Mine
Page 5: Foreword The Cargill Township Carbo
Page 8 and 9: TABLES 1. Table Of Lithologic Units
Page 11 and 12: Geology of Carbonatite - Alkalic Ro
Page 13 and 14: Introduction The Cargill Township C
Page 15 and 16: R. P. SAGE Township and extends int
Page 17 and 18: General Geology The Cargill Townshi
Page 19 and 20: R. P. SAGE A crandallite-rich blank
Page 21 and 22: R. P. SAGE more euhedral when in co
Page 23 and 24: Other Mafic to Ultramafic Rocks R.
Page 25: R. P. SAGE p. 116) as a mixture of
Page 29 and 30: R. P. SAGE mined thickness. Sandvik
Page 31 and 32: TABLE 2. STRATIGRAPHY OF OVERBURDEN
Page 33 and 34: R. P. SAGE containing approximately
Page 35 and 36: INTERNAL STRUCTURES R. P. SAGE The
Page 37 and 38: Economic Geology The Cargill Townsh
Page 39 and 40: R. P. SAGE Thoburn (1984) prepared
Page 41 and 42: Appendix A Petrographic Description
Page 43 and 44: R. P. SAGE Clinohumite is anhedral
Page 45 and 46: R. P. SAGE with brown cores and red
Page 47 and 48: R. P. SAGE hedral grains disseminat
Page 49 and 50: R. P. SAGE pyroxene and occurs alon
Page 51 and 52: R. P. SAGE grains disseminated thro
Page 53 and 54: TABLE A-2. MAJOR ELEMENT ANALYSES (
Page 55 and 56: TABLE A-2. CONTINUED. Ref. No. SiO2
Page 57 and 58: TABLE A-2. CONTINUED. Ref. No. SiO2
Page 59 and 60: R. P. SAGE TABLE A-3. TRACE ELEMENT
Page 61 and 62: TABLE A-3. CONTINUED. Ref. No. Ag A
Page 71 and 72: TABLE A-4. CONTINUED. Ref. No. QZ C
Page 77 and 78:
TABLE A-4. CONTINUED. Ref. No. QZ C
Page 79 and 80:
TABLE A-4. CONTINUED. Ref. No. QZ C
Page 81 and 82:
R.P. SAGE TABLE A-5. AVERAGE CHEMIC
Page 83 and 84:
Appendix B — Electron Microprobe
Page 85 and 86:
R.P. SAGE TABLE B-2. MICROPROBE MIN
Page 87 and 88:
R. P. SAGE TABLE B-3. MICROPROBE MI
Page 89 and 90:
TABLE B-5. MICROPROBE MINERAL ANALY
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
References Allen, C. 1972: The Petr
Page 99 and 100:
Index Aeromagnetic data, 7, 21, 24
Page 101 and 102:
Kinking Biotite, Rauhaugite, 18 Phl
Page 103:
Chart A — Cargill Carbonatite Com
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Cargill Township carbonatite complex, District of ... - Geology Ontario

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