Exploration for porphyry-style copper mineralisation near Llandeloy

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variation between pu8M microdioritn ?soda metasomatism (or potash metawmatirm) . 99.96% confidence lwel ties , , , 99% confidence level tlea (selected) . . 95% confidence lwel ties (selected) -7-7- comlation possibly spurious Conmcted from the comlation matrix derived from 39 borehole samples andyrsd for major rlemena weathering potash metasomatism Figure 35 Diagrammatic summary of positive inter- element correlations in igneous roclc samples from boreholes and their possible causes Table 11 Selected analyses of mineralised rocks from porphyry copper deposits , Si02 ;;g3 Fe as Fez03 MgO CaO Na2O K20 P205 S Cu Pb Zn Ni ?,l n Ba Rb Sr Zr Mean Median Max. Min. ---- 57.88 57.85 63.40 51.80 16.04 15.90 19.10 13.50 0.43 0.42 0.67 0.23 5.61 5.46 7.55 3.82 3.93 3.86 5.68 1.77 3.58 3.67 3.62 2.00 2.27 2.26 4.52 0.50 2.31 2.38 3.89 1.12 0.13 0.13 0.18 0.11 Major elements quoted as percent of oxide, trace elements as ppm. 1 - - - - 1450 740 7400 17 - - - - 36 3 7 7 0 17 - - - - 1200 1200 2100 700 - - - - - - - - - - - - - - - - 1 Coed y Brenin, dioritic rocks, phyllic zone, n=20 (Allen and others, 1976). 2 Panguna, Bougainville, average quartz diorite, propylitic and potash alteration, n=l7 (Ford, 1978). 3 Panguna, Bougainville, average leucocratic quartz diorite, propylitic and potash alteration, n=15 (Ford, 1978) 4 Bethlehem-Ja, British Columbis, mean granodiorite and quartz diorite, propylitic zone, n=16 (Olade and Fletcher, 1976 ; Olade, 1977) * indicates geometric mean. 5 Bethlehem-Ja, British Coluqbia, mean granodiorite and porphyry, potassic zone, n=6 (Olade and Fletcher, 1976; Olade, 1977) * indicates geometric mean. 2 3 ---- 61.05 - 61.68 16.92 0.53 5.66 2.08 4.08 4.13 1.79 0.20 6100 1500 5 49 6 400 236 4 3 638 109 64.22 15.19 0.33 5.81 1.36 1.93 4.95 2.76 0.12 3300 4100 2 3 4 4 2 00 134 3 5 566 9 1 4 - 4.09 1.97 3.17 4.42 1.77 - - 25 * - 205* 510* 41 * 686* - 5 65.08 - 1.86 0.74 1.48 2.91 3.84 - 10 - * 133* 560* 81* 235* -
propyli tic alteration all these elements are immobile, whilst under the more extreme conditions of potassic alteration Nb and Y show irregular mobility. No data are available for Sc whilst Ce and Th results above the detection limit are insufficient to reach a conclusion. Ratio plots of the type suggested by Beswick and Soucie (1978) permit an evaluation of the effects of metasomatism in remobilising and redistributing elements in varied lithologies provided that the unaltered rocks follow common igneous trends. Plots of this type (Fig. 36) together with simple 'stable1 element scattergrams (Fig. 37) of the type used by several authors (e.g. Pearce and Norry, 19791, indicate that whilst both Ti and Zr are depleted in a few samples (e.g. borehole 2, 25.25-26.82 m and 27.80-29.56 m) their ratio only shows moderate variation within a given rock type. As the silica content of these samples is heavily depressed compared with less altered rocks of similar type (due to extensive carbonate veining) it is suspected that the decrease in Ti and Zr is largely due to dilution. ~orphyhtic microtonalite Tonalite w Figure 36 Ratio plot of Ti/Rb v Zr/Rb for igneous rock samples 35 Y shows more erratic behaviour (Fig. 37) with two samples from borehole 2 depleted whilst one from borehole 5 is apparently enriched with respect to Zr or Ti, suggesting Y mobility in rocks which have suffered po tassic alteration. Statistics and elemental levels suggest that P and A1 may also have remained relatively immobile during alteration though small changes in P may be hidden by the relative imprecision of the analyses with respect to the total variation in the rocks. The Nb content of all rocks is low but is below the detection limit in a greater proportion of the rocks which have suffered K-feldspar alteration than can be readily attributed to chance, and it is believed that depletion during potash alteration may have taken place. These observations are supported by multivariate statistical analysis of the borehole data which show negative associations of the type Cu, S, Fe v Y and K20, Ba, Rb v Nb, Sr, NagO. Mobile/stable element plots of the type shown in Figure 36 can be useful indicators of the degree of
Page 1: Natural Environment Research Counci
Page 5: Report No. 78 @ Crown copyright 198
Page 9 and 10: SUMMARY REGIONAL STUDIES Intrusive
Page 11 and 12: SUMMARY Geological, geochemical and
Page 13 and 14: concluded that except for Zn the re
Page 15 and 16: The only rock containing evidence o
Page 17 and 18: Table 3 Analyses of miscellaneous r
Page 19: - 28 St. Brides Bay -
Page 22 and 23: Hercynian orogenies (M. 3. Arthur,
Page 24 and 25: Figure 14 Location of soil anomalie
Page 26 and 27: producing a very limited dispersion
Page 28 and 29: -1 00- Contours of VLF horizontal i
Page 30 and 31: area and periglacial and glacial de
Page 32 and 33: the Brunel Beds or the Tetragraptus
Page 34 and 35: contains sparse subhedral plagiocla
Page 36 and 37: There is some variation in the alte
Page 38 and 39: The cause of other isolated weak Cu
Page 40 and 41: j Table 9 Summary of analyses of in
Page 42 and 43: increase the Zr content. The divisi
Page 46 and 47: T/I~~/~~IPYS openjoi~~tcd limestone
Page 48 and 49: Table 13 Summary statistics for sed
Page 50 and 51: than average values quoted for sand
Page 52 and 53: Introduction The main geophysical m
Page 54 and 55: Figure 42 Contour map of apparent r
Page 56 and 57: Figure 45 Contour map of tow magnet
Page 58 and 59: Pigum? 47 Cumulative f reguency plo
Page 60 and 61: it to this late propylitic alterati
Page 62 and 63: HOLWSTER, V.F. 1974. An appraisal o
Page 64 and 65: APPENDIX 1 ABBREWATEI) BOREHOLB LOG
Page 66 and 67: BOREHOLE 2 Registration Number STvI
Page 68 and 69: BOREHOLE 3B Registration Number SM
Page 70 and 71: BOREHOLE 5 Registration Number SM 8
Page 76 and 77: SANDSTONE: as above CLAY GOUGE: SAN
Page 78 and 79: --- APPARENT ESISTIVITY pa IN OHM M
Page 80 and 81: APPARENT ESISTMTY H Bbs ys 06 q6 CH
Page 82 and 83: z ~ l ~ ~ ~ l ~ l . ~ l ~ , ~ l l A
Page 84 and 85: z ~ 1 ~ 1 ~ 1 ~ 1 ~ 1 APPARENT FEJS
Page 86 and 87: z ~ l $ l l l l l ~ l l ~ l l l l ~
Page 88 and 89: MAGNETIC FELD IN NAFTESLA Y /-*-.-.
Page 90 and 91: !IN@ a 8 g e s s I! s F N : , S ? I
Page 92 and 93: ~ N & E e 8 g B 8 8 7 a F N . S ~ 9
Page 94 and 95:
PHYSICAL PROPERTY MEASUREMENTS ON B
Page 96 and 97:
Borehole 8 (diameters of core 9-72
Page 98 and 99:
APPENDIX 5 COMPUTER MODELLING OF AE
Page 101 and 102:
RMS RESID - 6.53 FLU. PT ELEV ORS n
Page 103 and 104:
MRGNET I C: TIJTERF'HFTAT 1014 . .
Page 105 and 106:
ANU.YSB OF BOLPROLB CORE& TRACE ELE
Page 107 and 108:
. Sample BH , Depthv ,(m); -, - . ~
Page 109:
. , I , . . . . .. . , . , '," . ',
Page 112 and 113:
Fig.7 Aeromagnetic anomaly map of t
Page 115 and 116:
\ Fig.13. Compilation map of resist
Page 117 and 118:
Q Q E C E CCt C E Ct C Q Ct CtQ C Q
Page 119 and 120:
!2 CO N A 4 ul o ~n o ul 0 DEPTH IN
Page 121 and 122:
Fig.25 BOREHOLE 5 C C C C Ct C E K
Page 123 and 124:
Fig.27 BOREHOLE 7 E Q C Q E C 0 Q E
Page 125:
81 82 83 84 Fig.30. : Location of c
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Exploration for porphyry-style copper mineralisation near Llandeloy

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