U-Pb SHRIMP and <sup>40</sup>Ar/<sup>39</sup>Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, São Luís cratonic fragment, Brazil

Klein, Evandro Luiz; Tassinari, Colombo Celso Gaeta; Vasconcelos, Paulo Marcos

doi:10.5327/Z2317-4889201400020008

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Brazilian Journal of Geology

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Articles • Braz. J. Geol. 44 (2) • Apr-Jun 2014 • https://doi.org/10.5327/Z2317-4889201400020008 copy

U-Pb SHRIMP and ⁴⁰Ar/³⁹Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, São Luís cratonic fragment, Brazil

Geocronologia do depósito aurífero Paleoproterozoico orogênico do Caxias, fragmento cratônico São Luís, Brasil

Authorship SCIMAGO INSTITUTIONS RANKINGS

Caxias is an orogenic gold deposit in the São Luís cratonic fragment, which is correlated with the Rhyacian terranes of the West-African Craton. The deposit postdates peak metamorphism (estimated at 2100 ± 15 Ma) and is hosted in a shear zone that cuts across schists of the Aurizona Group (2240 ± 5 Ma) and the Caxias Microtonalite. The emplacement age of the microtonalite, as determined in this work by SHRIMP U-Pb zircon dating, is 2009 ± 11 Ma and represents a late-stage magmatic event in the São Luís cratonic fragment. Older zircon age of 2139 ± 10 Ma is interpreted as due to inheritance from the older granitoid or volcanic suites (magmatic sources?) or to contamination during emplacement. Lead isotope compositions indicate that the Pb incorporated in ore-related pyrite was probably sourced from regional, orogenic calc-alkaline granitoids of ca. 2160 Ma. Hydrothermal sericite from Caxias yielded a ⁴⁰Ar/³⁹Ar plateau age of 1990 ± 30 Ma, which combined with the emplacement age of the Caxias Microtonalite brackets the age of gold mineralization between 2009 ± 11 and 1990 ± 30 Ma.

orogenic gold; geochronology; isotope geochemistry

Spot	% Comm ²⁰⁶Pb	U (ppm)	Th (ppm)	²³²Th /²³⁸U	²⁰⁶Pb /²³⁸U Age (Ma)^c	1s	²⁰⁷Pb /²⁰⁶Pb Age (Ma)^c	1s	% Discord	²⁰⁷Pb /²⁰⁶Pb*	% Error	²⁰⁷Pb /²³⁵Pb*	% Error	²⁰⁶Pb /²³⁸Pb*	% Error	Error correl
Sample	EK1
1.1**	0.21	251	110	0.45	2235.5	66.7	2152	10	-4	0.1340	0.6	7.66	3.6	0.4145	3.5	0.991
2.1*	2.77	116	110	0.98	2043.8	64.8	2003	58	-2	0.1232	3.3	6.34	5.0	0.3731	3.7	0.784
3.1	0.84	222	125	0.58	1513.5	49.6	1960	23	29	0.1202	1.3	4.39	3.9	0.2646	3.7	0.702
4.1*	0.10	207	239	1.19	1936.6	59.5	2020	12	4	0.1244	0.6	6.01	3.6	0.3504	3.6	0.987
4.2*	0.12	312	147	0.49	2000.7	60.7	1993	10	0	0.1225	0.6	6.15	3.6	0.3639	3.5	0.990
5.1**	0.49	227	135	0.61	1981.5	60.3	2129	13	7	0.1323	0.8	6.56	3.6	0.3598	3.5	0.906
6.1**	0.07	63	19	0.30	2193.1	67.8	2126	19	-3	0.1321	1.1	7.38	3.8	0.4052	3.6	0.963
6.2*	0.23	63	19	0.31	2152.6	67.1	2132	22	-1	0.1326	1.2	7.25	3.9	0.3964	3.7	0.958
7.1**	2.55	289	66	0.23	1979.7	63.8	2044	58	3	0.1261	3.3	6.25	5.0	0.3595	3.7	0.904
8.1*	0.37	401	130	0.33	1965.5	59.8	2006	11	2	0.1234	0.6	6.06	3.6	0.3565	3.5	0.991
8.2**	0.00	321	74	0.24	2095.1	63.1	2023	8	-3	0.1246	0.5	6.60	3.6	0.3840	3.5	0.991
9.1	1.67	167	40	0.25	1430.4	47.7	2030	37	42	0.1251	2.1	4.28	4.3	0.2484	3.7	0.789
9.2	1.07	896	105	0.12	807.9	27.2	1381	42	71	0.0879	2.2	1.62	4.2	0.1335	3.6	0.891
10.1*	0.21	281	109	0.40	2151.6	64.6	2145	10	0	0.1335	0.6	7.29	3.6	0.3962	3.5	0.990
11.1**	1.96	1053	397	0.39	2096.1	62.8	2158	29	3	0.1346	1.7	7.13	3.9	0.3842	3.5	0.911
12.1*	0.70	147	58	0.40	2094.7	64.0	2108	18	1	0.1308	1.0	6.92	3.7	0.3840	3.6	0.975
12.2	5.07	882	205	0.24	802.8	26.6	1551	119	93	0.0961	6.3	1.76	7.3	0.1326	3.5	0.509
13.1*	0.46	381	81	0.22	2187.7	65.4	2146	11	-2	0.1336	0.6	7.44	3.6	0.4041	3.5	0.994
Sample	EK2
1.1	10.88	1317	228	0.18	839.2	29.0	1311	336	56	0.0848	17.3	1.63	17.7	0.1390	3.7	0.372
1.2	0.90	622	295	0.49	1920.8	58.4	2141	19	11	0.1332	1.1	6.38	3.7	0.3471	3.5	0.973
2.1	1.10	250	106	0.44	1967.0	59.9	2107	23	7	0.1306	1.3	6.43	3.8	0.3568	3.5	0.828
3.1	3.08	495	183	0.38	1469.5	46.3	1952	56	33	0.1197	3.2	4.23	4.7	0.2560	3.5	0.896
4.1	0.00	181	88	0.50	2298.1	68.6	2163	10	-6	0.1349	0.6	7.97	3.6	0.4283	3.6	0.981
5.1	10.93	957	296	0.32	902.6	30.4	1662	253	84	0.1021	13.6	2.12	14.1	0.1503	3.6	0.187
6.1	2.84	292	225	0.80	1833.9	56.5	2092	47	14	0.1296	2.7	5.88	4.4	0.3291	3.5	0.750
7.1	21.06	792	305	0.40	889.3	32.6	1946	439	119	0.1193	24.5	2.43	24.8	0.1479	3.9	0.058
8.1	2.31	525	94	0.19	1364.6	43.4	1902	44	39	0.1164	2.4	3.78	4.3	0.2358	3.5	0.837
9.1	13.42	1175	384	0.34	1050.6	35.1	1885	262	79	0.1153	14.6	2.81	15.0	0.1770	3.6	0.199
10.1	10.82	1047	687	0.68	706.7	24.0	1504	269	113	0.0938	14.2	1.50	14.7	0.1159	3.6	0.236
10.2	11.66	870	689	0.82	750.8	25.7	1471	303	96	0.0922	16.0	1.57	16.4	0.1235	3.6	0.875

Leaching step	²⁰⁶Pb/²⁰⁴Pb	2s	²⁰⁷Pb/²⁰⁴Pb	2s	²⁰⁸Pb/²⁰⁴Pb	2s	²⁰⁷Pb/²⁰⁶Pb
1	24.006	0.015	16.347	0.015	42.208	0.050	0.6800
2	22.203	0.014	16.121	0.015	41.119	0.050	0.7252
3	20.952	0.013	15.940	0.015	45.060	0.050	0.7599
4	20.714	0.014	15.900	0.016	45.660	0.060	0.7667
5	16.163	0.010	15.290	0.014	35.680	0.040	0.9451

run_ID	³⁶Ar/³⁹Ar	±	³⁷Ar/³⁹Ar	±	Ca/K	±	³⁸Ar/³⁹Ar	±	⁴⁰Ar/³⁹Ar	±	⁴⁰Ar*/³⁹Ar	±	Ar* (%)	±	Age (Ma)	±
4377-01A	0.1305	0.0061	1.49	0.42	2.92	0.83	0.0357	0.0049	562.00	15.00	524.00	14.00	93.09	0.34	1922.00	32.00
4377-01B	0.0265	0.0009	3.99	0.10	7.82	0.19	0.0176	0.0011	184.40	1.50	177.30	1.50	95.88	0.22	896.80	6.00
4377-01C	0.0191	0.0012	12.46	0.22	24.41	0.44	0.0164	0.0015	393.00	4.50	391.70	4.60	98.80	0.16	1597.00	12.00
4377-01D	0.0129	0.0010	11.63	0.20	22.80	0.39	0.0149	0.0012	424.90	4.90	425.40	5.00	99.31	0.15	1686.00	13.00
4377-01E	0.0087	0.0009	2.64	0.08	5.17	0.16	0.0062	0.0012	567.80	4.90	566.50	4.90	99.58	0.16	2017.00	10.00
4377-01F	0.0057	0.0006	0.19	0.04	0.37	0.08	0.0110	0.0007	566.70	4.70	565.10	4.70	99.70	0.12	2014.00	10.00
4377-01H	0.0044	0.0006	0.23	0.05	0.44	0.09	0.0133	0.0008	557.30	4.80	556.10	4.80	99.77	0.12	1994.00	10.00
4377-01I	0.0029	0.0006	0.23	0.05	0.44	0.09	0.0135	0.0008	544.40	5.20	543.60	5.20	99.85	0.14	1967.00	11.00
4377-01J	0.0011	0.0012	0.24	0.07	0.46	0.13	0.0109	0.0012	539.00	4.80	538.80	4.80	99.94	0.18	1956.00	11.00
4377-01K	0.0048	0.0011	0.36	0.09	0.71	0.17	0.0168	0.0015	548.30	5.40	547.00	5.40	99.75	0.21	1974.00	12.00
4377-01L	0.0072	0.0012	0.32	0.09	0.62	0.18	0.0152	0.0013	559.10	6.00	557.10	6.10	99.62	0.20	1996.00	13.00
4377-01M	0.0079	0.0009	0.70	0.08	1.36	0.16	0.0142	0.0011	560.50	5.60	558.40	5.60	99.59	0.13	1999.00	12.00
4377-01N	0.0130	0.0012	1.06	0.11	2.08	0.22	0.0183	0.0015	575.50	7.00	572.10	7.00	99.34	0.14	2029.00	15.00
4377-01O	0.0183	0.0018	1.70	0.16	3.33	0.31	0.0191	0.0020	582.40	9.10	577.70	9.10	99.08	0.17	2040.00	19.00
4377-01P	0.0152	0.0030	1.07	0.29	2.10	0.56	0.0141	0.0035	604.00	14.00	600.00	14.00	99.26	0.23	2088.00	30.00
4377-01Q	0.0182	0.0016	1.41	0.13	2.76	0.26	0.0195	0.0019	674.80	9.20	670.10	9.20	99.21	0.14	2226.00	18.00
4377-01R	0.0183	0.0026	1.69	0.20	3.30	0.39	0.0209	0.0026	681.00	14.00	677.00	14.00	99.22	0.18	2239.00	26.00
4377-02A	0.0699	0.0053	0.91	0.47	1.78	0.91	0.0249	0.0055	230.30	7.30	209.60	6.90	90.97	0.67	1022.00	26.00
4377-02B	0.0167	0.0018	7.06	0.25	13.83	0.48	0.0148	0.0019	321.60	5.20	318.70	5.20	98.62	0.24	1388.00	16.00
4377-02C	0.0064	0.0016	10.53	0.25	20.64	0.49	0.0150	0.0016	450.80	6.50	453.10	6.60	99.76	0.18	1756.00	16.00
4377-02D	0.0055	0.0012	1.35	0.11	2.65	0.21	0.0116	0.0013	558.60	6.90	557.60	6.90	99.73	0.16	1997.00	15.00
4377-02E	0.0042	0.0012	0.19	0.09	0.37	0.18	0.0137	0.0013	563.50	5.90	562.40	6.00	99.78	0.16	2008.00	13.00
4377-02F	0.0030	0.0010	-0.02	0.08	-0.04	0.15	0.0132	0.0012	564.30	5.10	563.40	5.10	99.84	0.12	2010.00	11.00
4377-02G	0.0033	0.0010	-0.04	0.07	-0.08	0.13	0.0120	0.0011	551.60	5.20	550.60	5.20	99.82	0.13	1982.00	11.00
4377-02H	0.0036	0.0008	0.07	0.06	0.13	0.11	0.0139	0.0009	552.00	4.30	551.00	4.30	99.81	0.11	1983.00	9.40
4377-02I	0.0044	0.0007	0.03	0.07	0.05	0.14	0.0139	0.0010	552.50	5.30	551.20	5.30	99.76	0.20	1983.00	12.00
4377-02J	0.0036	0.0009	0.01	0.08	0.01	0.15	0.0141	0.0010	549.70	5.00	548.60	5.10	99.80	0.18	1978.00	11.00
4377-02K	0.0038	0.0010	-0.02	0.07	-0.03	0.13	0.0140	0.0012	546.10	5.30	544.90	5.40	99.79	0.14	1970.00	12.00
4377-02L	0.0040	0.0009	0.31	0.08	0.60	0.16	0.0150	0.0010	554.20	5.50	553.20	5.50	99.79	0.15	1988.00	12.00
4377-02M	0.0057	0.0011	0.33	0.09	0.65	0.17	0.0147	0.0012	550.90	5.70	549.30	5.70	99.70	0.14	1979.00	13.00
4377-02N	0.0102	0.0024	0.78	0.18	1.52	0.35	0.0191	0.0027	572.00	12.00	570.00	12.00	99.48	0.18	2023.00	25.00
4377-02O	0.0090	0.0027	0.52	0.27	1.02	0.52	0.0225	0.0036	613.00	15.00	610.00	15.00	99.57	0.26	2108.00	30.00
4377-02P	0.0068	0.0017	0.48	0.16	0.95	0.32	0.0202	0.0020	616.00	11.00	614.00	11.00	99.68	0.22	2116.00	21.00
4377-02Q	0.0050	0.0028	0.74	0.28	1.45	0.55	0.0256	0.0034	600.00	14.00	598.00	14.00	99.76	0.22	2084.00	29.00
4377-02R	0.0052	0.0031	1.00	0.30	1.97	0.58	0.0201	0.0034	664.00	16.00	663.00	17.00	99.78	0.23	2213.00	32.00

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[1] * Corresponding author

Brasil

Brasil

U-Pb SHRIMP and 40Ar/39Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, São Luís cratonic fragment, Brazil

Geocronologia do depósito aurífero Paleoproterozoico orogênico do Caxias, fragmento cratônico São Luís, Brasil

U-Pb SHRIMP and ⁴⁰Ar/³⁹Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, São Luís cratonic fragment, Brazil