Genesis of the “soft” iron ore at S11D Deposit, in Carajás, Amazon Region, Brazil

Silva, Aline Cristina Sousa da; Costa, Marcondes Lima da

doi:10.1590/2317-4889202020180128

Acessibilidade / Reportar erro

Brasil

Brazilian Journal of Geology

Español English

Brasil

Español English

sumário « anterior atual seguinte »

Sumário

ARTICLE • Braz. J. Geol. 50 (1) • 2020 • https://doi.org/10.1590/2317-4889202020180128 copy

Genesis of the “soft” iron ore at S11D Deposit, in Carajás, Amazon Region, Brazil

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The origin of the soft ore at the S11D iron mine in Carajás was investigated using 20 samples from a diamond drill hole. The methods of analyses were X-ray diffraction (XRD), optical microscopy, whole-rock chemistry, and scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM/EDS). The drill hole presents a profile through the substratum (protore, a banded iron formation - BIF) and three weathering horizons, defined from the base to the top, saprolite (coarse and fine), and crust. The soft iron ore occurs distributed along the saprolite horizon, and it is composed mainly of hematite and subordinate magnetite. The amount of quartz decreases upwards, whereas the amount of Fe-Al-(Ti-P)-minerals increases towards the top. The total iron is enriched in the fine saprolite when compared to the protore (42.55 to 97.62 wt.% Fe₂O₃, respectively). Trace elements such as Zr, Cr, Y, and rare earth elements (REE) show relative enrichment upward because they are generally located in residual minerals (as zircon and anatase). The REEs in iron ore samples exhibit enrichment of light rare earth elements (LREE) and depletion of heavy rare earth elements (HREE), with pronounced positive Eu anomaly, which reaffirms the connection between iron ore and BIF. Based on the mineralogy, chemistry, textures, and structures, a genetic laterite-supergene model is proposed for the origin of soft ore at the S11D deposit.

KEYWORDS:
Banded iron formation-protore; lateritic profile; hematite; magnetite; geochemistry

			Crust			Fine saprolite			Coarse saprolite
COMP.	UNIT	DL	AbM1 (2)	AM3 (18.3)	AM4 (35)	AM8 (69)	AM13 (110)	AM17 (169)	AM20 (218)	AM22 (255)	AM24 (280)	AM29 (315.3)	AM36 (350)	AM37 (369)	AM45 (410)
SiO₂	%	0.01	1.02	5.66	0.41	0.64	0.99	5.56	47.08	55.88	5.76	39.11	0.55	40.64	3.44
Al₂O₃	%	0.01	1.51	11.26	16.24	3.13	0.75	4.31	0.16	0.31	0.21	0.15	0.09	0.12	0.05
Fe₂O₃	%	0.01	92.23	71.23	64.95	92.47	94.78	79.7	48.22	42.55	93.92	59.96	97.62	58.26	94.76
MnO	%	0.01	0.03	bdl	0.01	bdl	0.02	0.06	2.22	0.03	0.02	0.02	0.65	0.65	0.68
MgO	%	0.01	0.08	bdl	bdl	bdl	0.09	0.09	0.06	0.03	0.06	0.05	0.06	0.07	0.13
CaO	%	0.01	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Na₂O	%	0.01	bdl	bdl	0.01	bdl	bdl	0.06	bdl	0.01	0.01	0.01	0.24	bdl	0.01
K₂O	%	0.01	bdl	0.02	bdl	bdl	bdl	0.01	0.08	0.08	bdl	bdl	0.03	0.02	0.01
BaO	%	0.01	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Cr₂O₃	%	0.01	bdl	0.02	0.03	0.01	bdl	0.01	bdl	bdl	0.01	0.02	bdl	bdl	bdl
TiO₂	%	0.01	0.16	0.94	1.44	0.2	0.06	0.15	bdl	bdl	bdl	bdl	bdl	bdl	bdl
P₂O₅	%	0.01	0.37	0.3	1.68	0.22	0.09	0.22	0.01	0.01	0.01	bdl	0.01	bdl	bdl
SO₃	%	0.01	0.42	0.29	0.39	0.03	0.01	0.03	0.02	bdl	0.04	bdl	0.03	0.02	bdl
SrO	%	0.01	bdl	bdl	0.01	0.01	bdl	0.01	bdl	bdl	0.01	bdl	0.01	0.01	bdl
LOI	%	0.01	4.05	10.13	14.35	3.31	2.92	8.75	0.95	0.59	0.66	0.23	0.67	0.52	0.61
Total	%	0.01	99.92	99.94	99.65	100.10	99.73	99.12	99.08	99.5	100.80	99.58	100.05	100.45	99.80
C	%	0.01	0.21	0.8	0.14	0.05	0.07	0.08	0.07	0.06	0.08	0.04	0.05	0.05	0.06
S	%	0.01	0.01	0.08	0.01	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
F	ppm	20	50	80	90	50	50	70	bdl0	bdl0	40	40	bdl0	bdl0	bdl0
Cl	ppm	50	150	80	140	90	120	80	140	110	240	180	140	290	140
Li	ppm	0.1	0.1	0.2	0.1	0.1	0.1	0.2	0.2	0.1	0.2	0.1	0.1	0.2	0.2
Rb*	ppm	0.2	0.2	0.9	bdl	bdl	bdl	0.5	1.4	11.8	0.3	0.2	0.4	0.5	0.3
Cs*	ppm	0.01	0.02	0.08	bdl	bdl	0.01	0.01	0.01	0.08	0.01	0.01	bdl	0.01	0.01
Be	ppm	0.05	0.28	0.13	0.41	0.16	0.36	0.43	0.11	0.13	0.18	0.12	0.12	0.13	0.25
Sr*	ppm	0.1	3.4	5.3	51.3	6	2.2	31.8	10.9	1.4	1.9	1.4	13.9	4	10.5
B	ppm	10	10	10	10	10	10	10	bdl	bdl	bdl	bdl	10	bdl	10
Ge	ppm	0.05	1.91	1.34	0.38	1.39	2.11	1.59	0.38	0.28	1.29	1.96	0.85	0.51	0.86
As	ppm	0.1	1.8	4.2	0.9	0.7	0.8	3	1	1.6	2.4	3.3	1.3	1	1.6
Sb	ppm	0.05	0.18	0.32	0.71	0.41	0.18	0.1	0.07	0.16	0.35	0.08	0.2	0.07	0.22
Te	ppm	0.01	0.03	1.1	0.28	0.04	0.04	0.03	0.03	0.01	bdl	0.02	0.03	0.03	0.02
Sc	ppm	0.1	2.1	4.5	21.4	4.6	1.9	9	0.4	0.7	0.5	0.2	0.2	0.2	0.2
V*	ppm	5	22	173	378	131	17	55	bdl	6	14	bdl	bdl	bdl	17
Cr*	ppm	10	30	130	230	40	20	60	10	30	10	90	bdl	10	bdl
Co*	ppm	0.5	3.2	0.5	1.4	0.7	10.6	15.6	15.2	1.3	5	2.9	13.9	6.8	7.4
Ni	ppm	0.2	1	1.1	3.2	1.8	1.7	8.3	3.9	13.4	4.9	66.7	4.3	7.2	5.2
Cu	ppm	0.2	31.3	14.7	42.5	12.1	66.2	578	590	60.3	18.7	45	172.5	179.5	488
Zn	ppm	2	14	12	13	4	6	26	24	3	7	2	11	8	11
Y*	ppm	0.5	4.7	8.8	22.8	4.8	4.8	15.9	3.3	1.5	2.6	3	3.4	1.4	4.9
Zr*	ppm	2	37	278	357	50	11	30	bdl	5	2	bdl	2	2	bdl
Nb*	ppm	0.2	3.1	16	23.9	3	0.8	1.4	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Mo*	ppm	2	2	3	4	bdl	bdl	2	bdl	bdl	bdl	23	bdl	bdl	3
Ag	ppm	0.01	0.18	0.04	0.02	bdl	0.01	0.02	0.08	0.06	0.05	0.03	0.03	0.11	0.01
Cd	ppm	0.01	0.08	0.02	bdl	bdl	bdl	bdl	0.16	bdl	0.01	bdl	0.05	0.04	0.01
Hf*	ppm	0.2	1.1	7.6	10	1.6	0.3	0.8	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Ta*	ppm	0.1	0.2	1.2	1.7	0.2	0.1	0.1	bdl	bdl	bdl	bdl	bdl	bdl	bdl
W*	ppm	1	11	5	13	2	2	3	2	4	7	2	4	2	3
Re	ppm	0.001	0.001	bdl	0.001	0.001	bdl	0.001	bdl	0.001	0.001	0.001	bdl	bdl	bdl
Au	ppm	0.02	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Hg	ppm	0.01	0.18	0.28	0.06	0.02	0.02	0.03	0.02	0.02	0.02	0.02	0.01	0.02	bdl
Th*	ppm	0.05	3.14	12.45	26.8	4.28	1.04	1.87	bdl	0.31	0.06	bdl	0.07	bdl	0.05
U*	ppm	0.05	1.1	2.15	4.3	1.06	5.93	3.44	0.18	1.41	0.89	1.16	0.29	0.17	2.51
Ga*	ppm	0.1	4.3	20.6	47.1	6.4	2.4	6.9	0.9	1.1	0.3	0.3	0.4	0.4	0.5
In	ppm	0.005	0.026	0.08	0.19	0.034	0.008	0.026	bdl	0.008	0.005	bdl	0.011	0.006	0.015
Tl*	ppm	0.5	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
Pb	ppm	0.2	1.9	10.7	1.2	0.5	0.7	2.8	1.3	0.6	1.8	0.7	1.3	1.4	2.5
Sn*	ppm	1	1	3	7	1	1	1	bdl	1	1	bdl	bdl	bdl	bdl
Bi	ppm	0.01	0.09	0.43	0.17	0.13	0.05	0.13	0.06	0.04	0.09	0.03	0.07	0.07	0.15
Se	ppm	0.2	bdl	0.9	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl	bdl
La*	ppm	0.5	6.6	6.1	37.1	2.8	4.3	38.5	9.8	2.6	2.1	4	4	4.9	5.4
Ce*	ppm	0.5	8.2	10.3	74.1	10.3	9.5	42.6	6.4	4.6	2.8	4.5	4.6	4.1	5.2
Pr*	ppm	0.03	1.07	1.06	6.9	0.6	0.9	9.44	1.91	0.39	0.38	0.43	0.5	0.71	0.91
Nd*	ppm	0.1	3.3	3.4	22.5	2	3	32.2	7	1.2	1.4	1.1	1.8	2.5	3.9
Sm*	ppm	0.03	0.67	0.75	4.07	0.48	0.64	7.79	1.67	0.22	0.31	0.1	0.42	0.57	1.1
Eu*	ppm	0.1	0.22	0.19	1.02	0.17	0.24	2.89	0.68	0.09	0.17	0.11	0.25	0.25	0.49
Gd*	ppm	0.05	0.48	0.85	3.4	0.51	0.48	5.67	1.17	0.2	0.26	0.12	0.38	0.39	0.86
Tb*	ppm	0.01	0.08	0.18	0.6	0.09	0.08	0.93	0.18	0.03	0.04	0.02	0.05	0.06	0.14
Dy*	ppm	0.05	0.53	1.33	3.88	0.6	0.47	5.44	0.91	0.2	0.28	0.12	0.33	0.3	0.73
Ho*	ppm	0.01	0.11	0.29	0.81	0.15	0.11	1.01	0.15	0.05	0.05	0.03	0.06	0.05	0.13
Er*	ppm	0.03	0.35	1	2.38	0.45	0.35	2.73	0.36	0.12	0.16	0.13	0.2	0.14	0.36
Tm*	ppm	0.01	0.05	0.17	0.54	0.08	0.06	0.4	0.05	0.02	0.02	0.01	0.03	0.02	0.04
Yb*	ppm	0.03	0.38	1.21	2.31	0.56	0.37	2.62	0.32	0.13	0.12	0.1	0.16	0.11	0.23
Lu*	ppm	0.01	0.07	0.19	0.34	0.08	0.06	0.38	0.04	0.02	0.01	0.02	0.02	0.02	0.03
Eu/Eu*	ppm		1.19	0.73	0.84	1.05	1.32	1.33	1.49	1.31	1.83	3.07	1.91	1.62	1.54
Ce/Ce*	ppm		0.57	0.77	0.92	1.65	1.00	0.49	0.29	0.82	0.60	0.53	0.53	0.38	0.43
∑LREE			20.54	22.65	149.1	16.86	19.06	139.1	28.63	9.3	7.42	10.36	11.95	13.42	17.86
∑HREE			1.57	4.37	10.86	2.01	1.5	13.51	2.01	0.57	0.68	0.43	0.85	0.7	1.66
∑REE			22.11	27.02	160	18.87	20.56	152.6	30.64	9.87	8.1	10.79	12.8	14.12	19.52
Coarse Saprolite							Protore
COMP.	UNIT	DL	AM46 (434)	AM47 (455)	AM49b (466.5)	AM51 (476.5)	AM52 (490)	AM54 (522)	AM55 (524.5)	UCC	CH	BIF	Factor Min./Max.
SiO₂	%	0.01	0.48	0.5	4.61	0.48	42.82	45.99	50.39	66.6		44.6	0.01/0.84
Al₂O₃	%	0.01	0.21	0.14	0.32	0.21	0.33	1.16	0.26	15.4		0.63	0.00/1.05
Fe₂O₃	%	0.01	94.97	89.39	69.36	68.15	57.68	35.93	44.59	5.04		53.65	7.13/19.37
MnO	%	0.01	2.96	5.28	13.35	23.7	0.02	0.57	0.1	0.10		0.06	0.10/237.00
MgO	%	0.01	0.05	0.05	0.02	0.06	0.05	4.62	1.29	2.48		0.1	0.01/1.86
CaO	%	0.01	bdl	0.01	0.08	0.05	bdl	0.08	1.86	3.59		0.04	0.00/0.52
Na₂O	%	0.01	bdl	bdl	bdl	bdl	bdl	0.01	bdl	3.27		0.04	0.00/0.07
K₂O	%	0.01	0.18	0.12	0.29	1.18	bdl	0.05	bdl	2.80		0.04	0.00/0.42
BaO	%	0.01	bdl	0.52	1.32	0.29	bdl	bdl	bdl				/
Cr₂O₃	%	0.01	bdl	0.01	0.01	bdl	bdl	bdl	bdl				/
TiO₂	%	0.01	bdl	bdl	bdl	bdl	bdl	0.04	bdl	0.64		0.02	0.06/2.25
P₂O₅	%	0.01	0.01	0.09	0.39	0.02	0.01	0.02	0.01	0.15		0.01	0.07/11.20
SO₃	%	0.01	0.03	bdl	0.04	0.03	0.02	0.52	0.2				/
SrO	%	0.01	0.01	0.01	0.04	0.04	0.01	bdl	0.01				/
LOI	%	0.01	0.86	4.24	8.57	4.14	-0.13	11.4	1.51			0.73	/
Total	%	0.01	100.05	100.85	99.86	100.5	100.85	100.55	100.25	100.05		-	0.99/1.01
C	%	0.01	0.06	0.04	0.08	0.05	0.06	3.39	0.81				/
S	%	0.01	bdl	bdl	bdl	bdl	bdl	0.23	0.08	0.062			0.16/3.70
F	ppm	20	bdl	20	bdl	bdl	bdl	120	60	557			0.04/0.22
Cl	ppm	50	190	100	60	110	bdl	700	100	294			0.20/2.38
Li	ppm	0.1	0.2	0.3	0.1	0.2	0.2	0.2	0.2	24	1.44		0.00/0.01
Rb*	ppm	0.2	4.5	2.7	8.1	27.7	0.3	2.8	0.5	82	2.33		0.00/0.34
Cs*	ppm	0.01	0.04	0.04	0.12	0.12	0.04	0.16	0.04	4.9	0.189		0.00/0.03
Be	ppm	0.05	0.27	0.43	2.42	1.04	0.08	0.11	0.35	2.1	0.023		0.04/1.15
Sr*	ppm	0.1	53.7	41.7	345	273	0.9	5.2	4.9	320	7.74		0.00/1.08
B	ppm	10	10	10	bdl	bdl	10	10	10	17			0.59/0.59
Ge	ppm	0.05	1.09	1.35	1.93	0.84	0.9	1.23	0.93	1.4			0.20/1.51
As	ppm	0.1	1.8	3.9	100.5	3.8	1.9	3.7	2.3	4.8			0.15/20.94
Sb	ppm	0.05	0.22	0.07	0.17	0.2	0.2	0.06	0.2	0.4		7.43	0.15/1.78
Te	ppm	0.01	bdl	0.03	0.02	bdl	0.02	0.07	0.03				/
Sc	ppm	0.1	0.3	0.3	0.9	0.5	0.2	1.1	0.3	14.0	5.85	0.27	0.01/1.53
V*	ppm	5	bdl	5	13	57	bdl	7	bdl	97	52.4		0.05/3.90
Cr*	ppm	10	bdl	20	110	10	10	130	110	92	2627		0.11/2.50
Co*	ppm	0.5	15.1	32.3	208	149.5	1.5	4.6	8.1	17.3	520		0.03/12.02
Ni	ppm	0.2	1.3	12.1	51.3	4.3	0.9	42.6	67.2	47	11300	7.85	0.02/1.43
Cu	ppm	0.2	172.5	278	2250	1955	59.8	373	66.1	28	127	29.79	0.43/80.4
Zn	ppm	2	40	68	228	197	8	15	8	67	303	66.58	0.03/3.40
Y*	ppm	0.5	5.8	5.6	38	18.4	1.2	2.6	4.5	21	1.56		0.06/1.81
Zr*	ppm	2	2	bdl	bdl	bdl	bdl	24	2	193	3.52	16.89	0.01/1.85
Nb*	ppm	0.2	bdl	bdl	bdl	bdl	bdl	0.7	bdl	12	0.289		0.06/1.99
Mo*	ppm	2	bdl	bdl	5	bdl	bdl	2	2	1.1			1.82/20.91
Ag	ppm	0.01	0.01	0.04	1.54	0.29	0.02	0.08	0.05	53			0.00/0.03
Cd	ppm	0.01	0.01	0.18	0.5	1.32	bdl	0.01	0.01	0.09			0.11/14.67
Hf*	ppm	0.2	bdl	bdl	bdl	bdl	bdl	0.7	bdl	5.3	0.107		0.06/1.89
Ta*	ppm	0.1	bdl	bdl	bdl	bdl	bdl	0.1	bdl	0.9	0.015		0.11/1.89
W*	ppm	1	3	2	1	1	1	1	1	1.9	0.11		0.53/6.84
Re	ppm	0.001	0.001	0.001	bdl	bdl	bdl	0.002	bdl	0.198			0.01/0.01
Au	ppm	0.02	bdl	bdl	0.04	0.04	0.03	0.03	0.03	1.5			0.02/0.03
Hg	ppm	0.01	0.01	0.05	0.46	0.08	bdl	0.01	bdl	0.05			0.20/9.20
Th*	ppm	0.05	0.17	bdl	bdl	bdl	bdl	1.69	0.23	10.5	0.028		0.00/2.55
U*	ppm	0.05	1.91	0.67	1.96	2.34	0.28	0.58	0.34	2.7	0.008		0.06/2.20
Ga*	ppm	0.1	1	2.5	7.3	10.8	0.4	1.6	0.9	17.5	9.48		0.02/2.69
In	ppm	0.005	0.033	0.006	bdl	0.037	0.008	0.042	0.015	0.056			0.09/3.39
Tl*	ppm	0.5	bdl	5.7	11.6	1.1	bdl	bdl	bdl	0.9			1.22/12.89
Pb	ppm	0.2	2.4	2	2	5.2	0.6	1.1	0.7	17	2.69	18.33	0.03/0.63
Sn*	ppm	1	bdl	bdl	bdl	bdl	bdl	1	bdl	2.1			0.48/3.33
Bi	ppm	0.01	0.11	0.05	0.02	0.13	0.01	0.37	0.17	0.16		6.2	0.06/2.69
Se	ppm	0.2	bdl	bdl	0.4	0.8	bdl	0.4	bdl	0.09			4.44/10.00
La*	ppm	0.5	4.9	5.9	46.4	46.6	1.1	2.3	7.1	31	0.235		0.04/1.50
Ce*	ppm	0.5	5.9	4.6	13.3	6.1	1.4	3.7	11.4	63	0.6	2.38	0.02/1.18
Pr*	ppm	0.03	0.93	0.73	9.69	11.35	0.16	0.41	1.25	7.1	0.091		0.02/1.60
Nd*	ppm	0.1	3.7	3.2	40.6	47.6	0.6	1.6	4.2	27	0.464	1.9	0.02/1.76
Sm*	ppm	0.03	0.87	0.86	8.43	13.2	0.11	0.29	0.69	4.7	0.153	0.25	0.02/2.81
Eu*	ppm	0.1	0.48	0.28	3.62	5.52	0.07	0.09	0.2	1.0	0.059	0.17	0.07/5.52
Gd*	ppm	0.05	1.25	0.68	8.67	9.49	0.1	0.29	0.59	4.0	0.206	0.25	0.03/2.37
Tb*	ppm	0.01	0.19	0.12	1.08	1.24	0.01	0.03	0.08	0.7	0.038		0.01/1.77
Dy*	ppm	0.05	1.12	0.71	5.49	5.2	0.06	0.25	0.5	3.9	0.254		0.02/1.41
Ho*	ppm	0.01	0.2	0.15	0.97	0.78	0.01	0.06	0.1	0.83	0.057		0.01/1.22
Er*	ppm	0.03	0.5	0.45	2.59	1.85	0.04	0.25	0.29	2.3	0.166		0.02/1.19
Tm*	ppm	0.01	0.05	0.04	0.35	0.27	bdl	0.04	0.04	0.30	0.026		0.03/1.80
Yb*	ppm	0.03	0.35	0.31	2	1.51	0.04	0.24	0.26	2.0	0.168	0.15	0.02/1.31
Lu*	ppm	0.01	0.04	0.05	0.3	0.22	0.01	0.03	0.03	0.31	0.025	0.02	0.03/1.23
Eu/Eu*	ppm		1.41	1.12	1.29	1.51	2.04	0.95	0.96
Ce/Ce*	ppm		0.54	0.35	0.13	0.06	0.59	0.73	0.74
∑LREE			18.03	16.25	130.7	139.9	3.54	8.68	25.43
∑HREE			2.45	1.83	12.78	11.07	0.17	0.9	1.3
∑REE			20.48	18.08	143.5	150.9	3.71	9.58	26.73				5.27

Sociedade Brasileira de Geologia R. do Lago, 562 - Cidade Universitária, 05466-040 São Paulo SP Brasil, Tel.: (55 11) 3459-5940 - São Paulo - SP - Brazil
E-mail: sbgeol@uol.com.br

Acompanhe os números deste periódico no seu leitor de RSS

[1] *Corresponding author.