Cretaceous igneous-related mineralisation in the Reefton Goldfield, New Zealand

Figures & data

Figure 1. Location map of the area of study showing generalized geology. Modified from Nathan et al. (2002).

Figure 2. Map and cross-section of lower Blackwater Creek illustrating the structural features and mineralisation of the valley.

Figure 3. Blackwater dike textures. (A) and (B) display hand specimens of the dike. There is some feldspar colour change associated with sausseritic and/or sericitic alteration. (C) Cross-polarised light image of a zoned plagioclase phenocryst. (D) A back-scattered electron image of a coarse plagioclase within hornfelsic Greenland Group. Ser, sericite; Qtz, quartz; Bt, biotite; Musc, muscovite. (E) Hans specimen showing the dike to be cut by narrow quartz-pyrite veins. (F) A reflected light microscope image shows prominent pyrite, arsenopyrite (Aspy) and molybdenite (Mo).

Figure 4. Greenland Group textures. (A) Plane-polarised light image of typical Greenland Group meta-greywacke to the east of the Blackwater porphyry dike. Black lines indicate pressure solution seams. Metamorphic minerals are muscovite (Musc) and chlorite (Chl). (B) Hand specimen of spotted hornfels from adjacent to the dike. The spots are biotite (Bt). (C) Hand specimen from west of the dike showing ductilely deformed Greenland Group. (D) Hand specimen of Greenland Group west of the dike showing pyrite (Py) porphyroclasts as well as carbonate (Cc) veins (typically running across the field of view) and abundant spherical to oblate pale-coloured carbonate spots. (E) Cross-polarised light image showing the pyrite grains and carbonate spots. The pyrite has quartz strain fringes.

Figure 5. Mineralisation textures. (A) Hand specimen showing bleached Greenland Group formed by biotite destruction adjacent to quartz (Qtz)-pyrite (Py) veins. (B) Hand specimen of a quartz vein cutting spotted hornfelsic Greenland Group. This sample contains abundant molybdenite (Mo) and pyrite at its margin. (C) Back-scattered electron image showing molybdenite growing in fine bundles around pyrite. (D) Back-scattered electron image of a chloritised patch of biotite containing small patches of chalcopyrite (Chc), sphalerite (Sph), galena (Gal) and millerite (Mil). Phases were confirmed by semi-quantitative EDS analysis.

Figure 6. LA-ICP-MS Au, As and Pb trace element measurements on pyrite grains in different settings shows that those from the ductiley deformed Greenland Group contain the highest concentrations of Au and, typically, Pb.

Table 1. Pyrite trace elements by LA-ICP-MS. bdl, below detection limit.

Rock	spot	Au (ppm)	As (ppm)	Pb (ppm)
Greenland Group ductile deformation-related
BW15	15AM-1	0.2	490	135
BW15	15AM-2	0.3	465	672
BW15	15AM-3	0.2	303	165
BW20	20AM-1	3.3	6421	99
BW20	20AM-2	3.2	7683	75
BW20	20AM-3	4.2	11475	101
Propylitic-altered Blackwater Porphyry
BWT6A	T6A V-1	bdl	0.62	0.15
BWT6A	T6A V-2	bdl	0.80	0.04
BWT6A	T6A V-3	0.003	1.14	1.33
BWT6G	T6G-1	0.006	0.43	0.05
BWT6G	T6G-2	0.001	1.13	bdl
BWT6G	T6G-3	bdl	0.47	0.01
Phyllic-altered Blackwater Porphyry
BW12	T12AG-1	0.01	3.4	2.8
BW12	T12AG-2	0.01	0.2	0.8
BW12	T12AG-3	0.04	3.1	1.8
Quartz-sulphide veins in Greenland Group
BW18	T18A V-1	0.01	731	1
BW18	T18A V-2	0.48	1733	137
BW35	35A V-1	bdl	bdl	0.01
BW35	35A V-2	bdl	0.3	1
BW35	35A V-3	bdl	0.1	0.1
BW30	30AR-1	0.02	5.4	5
BW30	30AR-2	0.12	149	21
BW30	30AR-3	0.19	45	48
BW30	30AR-D5	0.16	60	116

Figure 7. Probability density and histogram diagram showing Early Cretaceous zircon U-Pb dates from the Blackwater dike.

Table 2. Zircon U-Th-Pb data for Blackwater dike.

				Measured isotope ratios and 1σ internal errors (%)								^a208Pb-corrected (*) dates and 1σ absolute internal errors (Ma)									^208Pb-corrected ages and errors (Ma)
Spot #	^aPb*	U	Th	^206Pb	±	^207Pb	±	^207Pb	±	^208Pb	±	^206Pb*	±	^207Pb*	±	^207Pb*	±	^a206Pb*/^238U	Common ^206Pb (%)	MSWD	^bDates	±
	(ppm)	(ppm)	U	^238U		^235U		^206Pb		^232Th		^238U				^206Pb*		^207Pb*/^235U concordance (%)
30	75.39	4555	0.27	0.01672	1.2	0.1296	2.4	0.0562	2.1	0.00607	3.2	106.4	1.3	115.4	4.8	304.7	11.2	92	0.47	13.68	106.4	3.0
15	17.11	1005	0.16	0.01785	0.7	0.1202	2.7	0.0488	2.6	0.00555	2.4	114.1	0.8	116.2	3.3	157.9	4.2	98	-0.05	1.98	114.1	3.1
07	15.34	904	0.14	0.01788	0.6	0.1199	2.2	0.0486	2.2	0.00592	2.6	114.2	0.7	113.4	2.8	98.3	2.3	101	0.08	2.30	114.2	3.0
21	6.12	363	0.09	0.01798	0.7	0.1242	3.1	0.0501	3.0	0.00665	4.0	114.6	0.8	114.5	3.7	112.9	3.6	100	0.22	1.35	114.6	3.1
13	29.73	1719	0.17	0.01809	0.5	0.1229	1.4	0.0493	1.3	0.00569	1.5	115.6	0.5	118.1	1.8	167.3	2.4	98	-0.02	2.99	115.6	3.0
01	11.48	664	0.17	0.01811	0.8	0.1256	2.4	0.0503	2.3	0.00593	2.4	115.6	0.9	118.7	3.0	180.5	4.3	97	0.07	3.10	115.6	3.1
03	17.21	996	0.15	0.01813	0.7	0.1234	1.9	0.0493	1.8	0.00606	2.2	115.7	0.8	115.9	2.4	119.1	2.3	100	0.11	2.87	115.7	3.1
11	20.28	1166	0.18	0.01813	0.6	0.1275	1.8	0.0510	1.7	0.00599	1.9	115.7	0.7	119.4	2.4	193.5	3.6	97	0.12	2.59	115.7	3.1
10	17.12	944	0.28	0.01835	0.5	0.1268	2.0	0.0501	1.9	0.00583	1.4	117.2	0.6	120.8	3.1	191.9	4.7	97	0.02	2.32	117.2	3.1
04	9.27	535	0.10	0.01848	0.7	0.1269	2.4	0.0498	2.3	0.00636	2.7	117.9	0.8	118.5	2.9	130.4	3.1	99	0.14	1.80	117.9	3.1
06	17.79	985	0.23	0.01853	0.6	0.1266	2.2	0.0495	2.2	0.00605	1.4	118.2	0.7	118.8	2.8	129.1	2.9	100	0.11	1.97	118.2	3.1
09	14.05	769	0.26	0.01860	0.5	0.1255	1.8	0.0490	1.8	0.00601	1.4	118.7	0.6	118.1	2.6	107.4	2.3	100	0.10	1.52	118.7	3.1
08	5.27	279	0.38	0.01859	1.5	0.1180	6.3	0.0460	6.1	0.00587	3.9	118.8	1.8	113.1	8.4	8.7	0.7	105	0.01	1.98	118.8	3.5
23	14.61	831	0.12	0.01869	0.7	0.1281	1.9	0.0497	1.8	0.00602	2.5	119.3	0.8	121.8	2.4	170.2	3.2	98	0.03	2.73	119.3	3.2
27	14.89	846	0.13	0.01867	0.7	0.1262	2.1	0.0490	1.9	0.00562	2.5	119.4	0.8	122.6	2.5	185.0	3.5	97	-0.09	2.38	119.4	3.2
24	8.47	457	0.30	0.01871	0.7	0.1261	2.5	0.0489	2.4	0.00570	2.0	119.7	0.9	123.9	3.6	205.2	5.5	97	-0.16	2.02	119.7	3.2
25	15.00	829	0.19	0.01881	1.0	0.1338	2.9	0.0516	2.7	0.00623	4.0	119.8	1.3	122.3	9.6	170.8	12.9	98	0.26	2.28	119.8	3.4
12	19.52	1082	0.18	0.01878	0.6	0.1267	1.5	0.0489	1.4	0.00615	1.6	119.8	0.7	119.2	2.2	106.6	1.9	101	0.10	2.96	119.8	3.2
22	7.70	423	0.21	0.01878	0.6	0.1269	2.9	0.0490	2.8	0.00595	2.4	119.9	0.8	121.2	3.7	146.6	4.3	99	0.00	1.34	119.9	3.2
14	10.87	564	0.41	0.01879	1.6	0.1193	4.7	0.0460	4.4	0.00598	3.7	120.0	1.9	114.1	6.7	8.0	0.5	105	0.01	3.22	120.0	3.6
26	13.70	693	0.47	0.01896	0.9	0.1358	2.5	0.0520	2.3	0.00627	1.4	120.7	1.1	122.6	4.3	158.9	5.4	98	0.33	2.95	120.7	3.3
28	5.77	290	0.48	0.01908	0.9	0.1322	3.7	0.0503	3.6	0.00603	2.0	121.8	1.1	125.6	5.8	197.7	8.7	97	0.02	1.91	121.8	3.3
05	25.09	1372	0.18	0.01909	0.6	0.1309	1.4	0.0497	1.3	0.00619	1.4	121.8	0.7	123.5	1.8	155.3	2.1	99	0.07	3.42	121.8	3.2
18	6.30	338	0.21	0.01923	0.8	0.1241	3.1	0.0468	2.9	0.00598	2.5	122.8	1.0	120.1	4.0	68.6	2.3	102	-0.07	1.74	122.8	3.3
16	12.58	653	0.31	0.01933	0.6	0.1275	2.1	0.0478	2.0	0.00628	1.9	123.3	0.8	120.0	4.0	57.3	1.9	103	0.09	2.12	123.3	3.3
15	9.17	479	0.26	0.01943	1.2	0.1327	3.5	0.0496	3.3	0.00656	3.5	123.6	1.5	120.1	7.0	53.0	3.1	103	0.31	2.57	123.6	3.5
14	18.25	488	0.32	0.03750	1.1	0.3180	2.8	0.0615	2.5	0.01217	2.4	237.0	2.7	275.0	8.3	612.0	14.9	86	0.16	2.94	237.0	6.7
17	45.71	577	0.18	0.08134	1.1	1.0073	2.1	0.0898	1.8	0.04029	2.8	496.3	5.5	623.0	13.5	1114.9	18.0	80	1.61	7.56	496.3	13.9
02	56.64	554	0.23	0.10369	0.9	1.0696	1.8	0.0748	1.5	0.03868	1.6	631.6	5.4	691.4	11.2	891.0	12.2	91	0.73	5.53	631.6	17.1
17	63.69	557	0.24	0.11542	0.7	1.5646	1.5	0.0983	1.3	0.05079	2.7	694.0	4.9	865.9	11.9	1336.0	14.1	80	1.52	2.85	694.0	18.5
02	50.70	450	0.21	0.11535	0.7	1.1709	1.6	0.0736	1.4	0.03677	2.1	703.0	4.4	779.4	9.7	1004.8	10.6	90	0.11	3.46	703.0	18.6
29	81.61	384	0.24	0.21264	0.9	3.0856	1.0	0.1052	0.6	0.07116	1.1	1238.4	9.7	1401.7	9.8	1659.5	7.8	88	0.39	1.58	1659.5	35.5
19	69.10	213	0.20	0.32160	0.7	5.9415	0.9	0.1340	0.7	0.09413	1.6	1797.4	10.3	1966.8	8.4	2150.0	6.4	91	0.01	1.56	2150.0	45.3
20	355.28	873	0.14	0.40083	0.5	8.0852	0.7	0.1463	0.4	0.11328	1.2	2172.9	10.6	2240.8	12.6	2303.5	11.5	97	0.00	2.24	2303.5	49.4

^aPb* = ²⁰⁸Pb-corrected value; ^bItalicised ages are those used to calculate the magmatic age.

Figure 8. Summary of mineral textures, paragenesis and events recorded or inferred from the rocks examined in lower Blackwater Creek.

Nathan S, Rattenbury MS, Suggate RP. 2002. Geology of the Greymouth area: scale 1:250,000. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences 1:250,000 geological map 12: 58p.

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