Geochemical characteristics and genetic analysis of BIF iron deposit background of Xincai iron deposit in He'nan Province
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摘要:
新蔡铁矿床位于华北克拉通南缘舞阳-霍邱铁矿成矿带中部, 矿体赋存于新太古代太华岩群变质岩系中。铁矿体主要呈层状、似层状, 局部为透镜状。矿石构造主要为条带状, 少量浸染状及块状。矿石主要由TFe2O3和SiO2组成, 其次为MgO和CaO, Al2O3及其他如Na2O、K2O、P2O5、TiO2、MnO含量大多小于0.1%。微量及稀土元素分析结果显示, 大离子亲石元素Sr和高场强元素Nb、Ta、Zr、Hf、Ti明显亏损, 此外Rb、U、La、Pb、Eu元素具正异常, Ti/V值平均24.13, 稀土元素总量较低, 平均为12.8×10-6。经PAAS标准化后, 铁矿石均表现为重稀土元素相对轻稀土元素富集((La/Yb)PAAS=0.43~0.79, 平均值0.55), 具有明显的La正异常(La/LaPAAS*平均值1.15)、Eu正异常(Eu/Eu*平均值2.88)和Y异常(Y/YPAAS*平均值1.68), 微弱的Ce负异常(Ce/CePAAS*平均值0.90)。较高的Y/Ho值(平均值44)说明含铁建造形成于相对缺氧的古海洋环境, 成矿物质主要来源于与海底火山活动相关的高温热液和海水的混合溶液。对矿体围岩斜长角闪岩原岩恢复及构造环境判别结果显示, 斜长角闪岩原岩为弧后盆地玄武岩, 代表其形成于弧后盆地的构造环境, 这也基本代表了本区含铁建造沉积时的构造环境。综合分析认为, 新蔡铁矿属于与弧后盆地火山活动密切相关的Algoma型BIF。
Abstract:The Xincai iron deposit is located in the middle part of the Wuyang-Huoqiu iron ore belt on the southern margin of the North China Craton.The ore body is hosted in the Late Archean Taihua Group metamorphic rock series.The iron ore body is mainly lamellar and partially lenticular.The ore structure is mainly banded, with a small amount of disseminated and massive ores.iron ore is mainly composed of TFe2O3 and SiO2, followed by MgO and CaO, and Al2O3 and others such as Na2O, K2O, P2O5, TiO2 and MnO are mostly less than 0.1%。Trace and rare earth element analytical results show that large ionic lithophile element such as Sr, high field strength elements such as Nb, Ta, Zr, Hf and Ti are significantly depleted, in addition, Rb, U, La, Pb, Eu elements are abnormal, and the average Ti/V ratio is 24.13, the total amount of rare earth elements is relatively low, and the average ∑REE is 12.8×10-6.After being standardized by PAAS, iron ore shows enrichment in light rare earth elements ((La/Yb) PAAS=0.43~0.79, average 0.55), with obvious La positive anomaly (La/LaPAAS* average 1.15), Eu positive anomalies (Eu/Eu* average 2.88), Y abnormalities (Y/YPAAS* average 1.68), and weak Ce negative anomalies (Ce/CePAAS* average 0.90).A relatively high Y/Ho value (average of 44) indicates that iron-bearing formation was formed in a relatively hypoxic palaeo-marine environment, and the ore-forming materials were mainly derived from the mixing of high-temperature hydrothermal fluids and seawater associated with volcanic activity on the sea floor.The results for the ore-bearing amphibolite analysis and the tectonic setting for the formation of the orebodies show that the protolith of amphibolite should be a post-arc basin basalt, which represents the tectonic setting of the amphibolite formed in the back-arc basin.The tectonic environment of the amphibolite also basically represents the tectonic environment when the iron-bearing formation was deposited in this area。According to the comprehensive analysis, Xincai iron mine belongs to Algoma type BIF closely related to volcanic activities in the back-arc basin.
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Key words:
- strip iron construction /
- magnetite /
- genesis of deposit /
- Xincai, He'nan Province
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表 1 练村铁矿矿石主量、微量和稀土元素组成及相关参数
Table 1. Composition and related parameters of major, trace and rare earth elements in Liancun iron ore
岩性 磁铁角闪石英岩 样品号 练31 练32 练33 练34 练35 练36 练37 练38 TFe2O3 47.79 40.77 47.92 47.69 49.88 45.42 42.76 53.13 SiO2 45.47 45.28 43.26 41.31 40.93 47.23 46.27 40.43 Al2O3 0.39 1.87 0.33 1.64 0.80 0.66 0.76 0.48 MgO 0.46 1.24 1.88 1.88 2.15 1.23 1.77 1.42 CaO 1.32 2.44 2.18 3.06 1.91 1.77 1.38 2.91 Na2O 0.078 0.064 0.037 0.051 0.026 0.050 0.062 0.020 K2O 0.18 0.88 0.034 0.46 0.19 0.062 0.36 0.043 P2O5 0.055 0.14 0.19 0.11 0.10 0.10 0.12 0.089 TiO2 0.025 0.14 0.018 0.075 0.072 0.042 0.038 0.032 MnO 0.076 0.063 0.093 0.13 0.22 0.066 0.092 0.19 Li 6.65 3.52 0.57 5.99 0.82 1.38 8.83 0.24 Be 0.36 0.81 0.11 0.22 0.30 0.04 0.56 0.12 P 362 670 974 488 531 520 899 485 Sc 0.44 1.68 0.31 0.98 0.99 0.65 1.04 0.45 Ti 138 571 65.5 357 284 192 220 123 V 8.65 19.10 4.26 12.80 10.30 6.42 8.09 6.38 Cr 5.32 10.50 3.83 5.13 24.00 4.52 8.35 3.73 Mn 752 445 690 901 1620 453 895 1330 Co 4.95 5.32 4.45 4.95 4.68 4.71 5.31 3.63 Ni 3.38 6.77 3.21 5.14 4.54 2.62 5.17 3.15 Cu 1.77 6.56 1.48 11.80 1.59 1.01 1.31 0.63 Zn 10.80 11.80 9.55 25.80 15.20 15.30 15.30 12.00 Ga 1.26 3.12 0.84 3.45 1.70 3.87 1.97 1.36 Ge 3.18 4.66 1.72 2.45 3.20 1.59 3.60 3.05 Rb 16.50 65.2 1.15 25.3 7.77 2.10 34.6 1.55 Sr 24.5 95.9 41.7 24.8 22.1 13.8 26.5 73.4 Y 2.80 6.22 6.09 4.71 4.57 4.97 7.47 3.80 Zr 5.73 20.0 4.27 10.4 8.94 5.36 7.54 2.93 Nb 0.36 1.21 0.14 0.26 0.47 0.17 0.55 0.28 Mo 0.13 0.16 0.10 0.16 0.66 0.18 0.29 0.09 Sn 0.21 0.22 0.09 0.19 0.17 0.12 0.31 0.11 Cs 3.25 5.21 0.12 2.19 0.27 0.27 3.06 0.10 Ba 68.6 82.9 9.34 40.0 26.2 4.66 62.7 7.94 Hf 0.15 0.49 0.09 0.27 0.23 0.14 0.22 0.08 Ta 0.02 0.04 0.01 0.02 0.02 0.02 0.06 0.02 Pb 1.52 5.23 1.05 2.68 3.68 1.24 0.88 1.39 Th 0.26 0.58 0.11 0.49 0.27 0.24 0.81 0.16 U 0.09 0.30 0.07 0.24 0.11 0.02 0.24 0.06 Sm/Yb 1.24 1.76 1.27 1.72 1.17 0.94 1.22 1.24 Eu/Sm 0.61 0.47 0.67 0.47 0.66 0.78 0.60 0.63 Sr/Ba 0.36 1.16 4.46 0.62 0.84 2.96 0.42 9.24 Ti/V 15.95 29.90 15.38 27.89 27.57 29.91 27.19 19.28 La 1.65 4.08 1.84 3.49 2.56 2.30 2.93 1.46 Ce 2.76 8.03 3.30 6.67 4.58 3.99 5.46 2.83 Pr 0.32 0.99 0.43 0.79 0.55 0.46 0.66 0.36 Nd 1.23 3.94 1.80 3.04 2.12 1.82 2.66 1.49 Sm 0.23 0.80 0.40 0.57 0.40 0.34 0.58 0.31 Eu 0.14 0.38 0.27 0.26 0.26 0.27 0.35 0.20 Gd 0.26 0.83 0.51 0.57 0.46 0.41 0.69 0.35 Tb 0.04 0.12 0.08 0.08 0.07 0.07 0.11 0.05 Dy 0.25 0.74 0.52 0.52 0.46 0.48 0.70 0.35 Y 2.8 6.22 6.09 4.71 4.57 4.97 7.47 3.8 Ho 0.06 0.16 0.13 0.12 0.11 0.12 0.16 0.08 Er 0.19 0.48 0.37 0.34 0.34 0.38 0.50 0.26 Tm 0.03 0.07 0.05 0.05 0.05 0.06 0.08 0.04 Yb 0.19 0.46 0.31 0.33 0.34 0.37 0.47 0.25 Lu 0.03 0.07 0.05 0.05 0.06 0.05 0.08 0.04 ΣREE 7.36 21.15 10.06 16.88 12.36 11.13 15.42 8.07 LREE 6.33 18.22 8.03 14.81 10.47 9.18 12.64 6.64 HREE 1.04 2.93 2.03 2.07 1.89 1.95 2.78 1.42 LREE/HREE 6.10 6.22 3.96 7.17 5.54 4.71 4.54 4.67 (La/Yb)PAAS 0.65 0.66 0.43 0.79 0.55 0.46 0.46 0.43 Eu/EuPAAS* 2.93 2.34 3.04 2.33 3.10 3.47 2.80 3.03 Ce/CePAAS* 0.88 0.92 0.86 0.93 0.89 0.89 0.90 0.91 La/LaPAAS* 1.24 1.05 1.26 1.04 1.11 1.22 1.13 1.16 Y/YPAAS* 1.84 1.43 1.88 1.53 1.61 1.63 1.76 1.77 Pr/PrPAAS* 1.01 1.03 1.02 1.03 1.03 1.01 1.02 1.01 Y/Ho 47 38 48 41 41 41 46 46 注：La/LaPAAS* = LaPAAS(3×PrPASS-2×NdPASS)；Ce/CePAAS*=2CePAAS/(LaPAAS+PrPAAS); Pr/Pr* PAAS =2Pr PAAS /(Ce PAAS +Nd PAAS); Eu/EuPAAS*=Eu PAAS /(0.67Sm PAAS +0.33Tb PAAS); Y/Y* PAAS =2Y PAAS /(Dy PAAS +Ho PAAS); 标准化数据据参考文献[21-22]；主量元素含量单位为%, 微量和稀土元素含量单位为10-6 
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表 2 Algoma型和Superior型BIF铁矿类型判别[19]
Table 2. The BIFs contrast of Algoma and Superior types
判别标志 Algoma型 Superior型 形成时代 中新太古代为主，2.8~2.5 Ga为高峰期 古元古代为主，2.5~1.8 Ga为高峰期 含铁建造类型 与超基性、基性火山岩-火山沉积岩相关 与碎屑岩-碳酸盐岩相关 构造环境 岛弧、弧后盆地或扩张大洋中脊附近 被动大陆边缘，大陆架浅海环境，克拉通内部盆地 矿物相 主要为磁铁矿相 具有明显的相分带，可见磁铁矿、碳酸盐和赤铁矿相 变质相 绿片岩相—角闪岩相，混合岩化较强 一般为绿片岩相变，混合岩化不明显
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① 卢欣祥, 韩宁, 杨延伟, 等. 河南东秦岭-大别山及邻区花岗岩和主要金属矿产分布规律图. 2018.
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