低密度地球化学填图重现性定量评价:以中国钴为例

doi:10.13745/j.esf.sf.2024.10.34

摘要/Abstract

摘要：

低密度地球化学填图的重现性是开展全球尺度地球化学填图的核心科学问题之一,长期以来备受地球化学填图界的密切关注。但缺乏对低密度地球化学填图重现性定量评价的有效手段,对重现性的定量化认识一直相当薄弱。本研究利用中国地球化学基准计划(CGB)和区域化探扫面计划(RGNR)两种尺度钴元素数据,基于1 546个典型汇水域局部空间相关系数分析,对低密度地球化学填图重现性进行定量评价,探讨其空间分布特征与影响因素。研究结果表明,全国尺度上,相关性受到钴含量和地球化学景观条件的共同影响。局部尺度上,受到差异剥蚀影响。贫钴背景下(沉积物钴含量<13 μg/g),填图重现性指数R在0.4附近浮动,而富钴背景下(沉积物钴含量>13 μg/g),填图重现性指数R从0.4增加至0.6以上。岩溶区、热带雨林区和半干旱中低山丘陵景观区重现性指数R高达0.58~0.74。冲积平原和森林沼泽景观区重现性指数R小于0.32。本研究为低密度地球化学填图方法研究提供了定量评价指标,总体而言,低密度地球化学填图采样方法能较好地重现元素分布特征,在全球尺度地球化学填图中具有良好的应用前景。

关键词: 重现性, 低密度地球化学填图, 钴, 汇水域, 局部空间相关性分析

Abstract:

Robustness is a fundamental scientific concern in low-density geochemical mapping, which has long garnered close attention from mapping researchers. However, quantitative understanding of robustness has been lacking due to the lack of effective quantitative assessment methods. In this study, using cobalt element data from two low-density mapping sources—the China Geochemical Baselines project (CGB) and the Regional Geochemical National Reconnaissance project (RGNR)—robustness is quantitatively assessed based on 1546 representative catchments through the utilization of local spatial correlation coefficients; the spatial distribution features and influencing factors are also discussed. On a national scale, robustness was influenced by sediment cobalt (Co) content and geochemical landscape conditions; on a local scale, it was affected by differential erosion in cobalt-rich and Co-poor source areas. In Co-poor environments (sediment Co<13 μg/g) the robustness index (R) value fluctuated around 0.4, while in Co-rich environments (sediment Co>13 μg/g) it increased from 0.4 to above 0.6 with rising Co content. Regions such as karst terrains, tropical rainforests, and semi-arid low hills had R values as high as 0.58 to 0.74, whereas alluvial plains and forested swamp regions had R values below 0.32. This study provides a reference for quantitative evaluaton of low-density mapping, deomonstrating that low-density geochemical mapping has good robustness and promising prospect in the global-scale geochemical mapping.

Key words: robustness, low-density geochemical mapping, cobalt, catchment, GW correlations

中图分类号:

P596

刘东盛, 王学求, 聂兰仕, 张必敏, 周建, 刘汉粮, 王玮, 迟清华, 徐善法. 低密度地球化学填图重现性定量评价:以中国钴为例[J]. 地学前缘, 2025, 32(1): 23-35.

LIU Dongsheng, WANG Xueqiu, NIE Lanshi, ZHANG Bimin, ZHOU Jian, LIU Hanliang, WANG Wei, CHI Qinghua, XU Shanfa. Quantatitive robustness assessment of low-density geochemical mapping: An example of China’s cobalt[J]. Earth Science Frontiers, 2025, 32(1): 23-35.

图/表 14

表1 低密度地球化学填图重现性研究实例

Table 1 Case studies on robustness of low-density geochemical mapping

作者	地区	每个样品控制面积/km²			对比元素
作者	地区	密度1	密度2	密度3	对比元素
Shen和Yan^[17]	中国江西	1	1800		W
成杭新和谢学锦^[18]	中国浙江	1	100~1 000	1 000~10 000	Sb、As、Ag、Sn、Pb、Na₂O
王学求等^[3]	中国新疆	4	25	100	Au、Cu、Mn、As、Hg、U
Smith和Reimann^[4]	美国	航空辐射测量	6 000		K
Demetriades^[19]	希腊	1.77~2.74	500		Pb
Cicchella等^[11]	欧洲		5 000	20 000	CaO、Th、U
聂兰仕^[20]	中国黔西南	1	16~25	100	Au
Birke等^[21]	德国	1.3	380	5 000	Ba、Cu、Cr、Pb、U
Gosar等^[22]	斯洛文尼亚	4	25	625	Hg
程湘等^[23]	印度尼西亚	4	100		Au、Ag、Cu、Zn、Ni
Liu等^[13]	中国新疆	1	180	1 600	Au、As、Sb

图1 基于汇水域赋值原理示意图

Fig.1 Method of assigning concentration to catchment

图2 汇水域要素的低密度(CGB)与较高密度(RGNR)的lgCo(μg/g)含量散点图

Fig.2 Satter plot of Co contents in catchments by low- (CGB) and higher-density (RGNR) geochemical mapping

图3 重现性指数R的概率分布图箱体表示25%~75%;虚线表示1.5 IQR内的范围(IQR为四分位距);短线表示中位线;空心方块表示均值;实心方块表示异常值。

Fig.3 Probability distribution of robustness index (R) values

图4 重现性指数R的空间分布

Fig.4 Spatial distribution of R values

图5 重现性指数R与中国地球化学景观区分布(据文献[30])

Fig.5 Spatial distribution of geochemical landscapes of China and its relationship with R. Aapted from [30].

图6 重现性指数R与中国基性岩和酸性岩的空间分布(据文献[31])

Fig.6 Spatial distribution of basic and acidic rocks of China and its relationship with R. Adapted from [31].

表2 汇水域钴含量区间代号及其对应对钴含量

Table 2 Co contents in studied catchments

含量区间	RGNR Co含量/(μg·g^-1)	CGB Co含量/(μg·g^-1)
1	2.6~<6.3	1.0~<4.7
2	6.3~<7.7	4.7~<5.8
3	7.7~<8.8	5.8~<7.0
4	8.8~<9.6	7.0~<8.1
5	9.6~<10.3	8.1~<8.8
6	10.3~<11.0	8.8~<9.7
7	11.0~<11.7	9.7~<10.6
8	11.7~<12.1	10.6~<11.4
9	12.1~<13.0	11.4~<12.1
10	13.0~<13.7	12.1~<13.0
11	13.7~<14.7	13.0~<14.1
12	14.7~<15.5	14.1~<15.1
13	15.5~<16.7	15.1~<16.6
14	16.7~<18.6	16.6~<18.6
15	18.6~<60.6	18.6~<80.8

图7 沉积物钴含量与R值关系

Fig.7 Relationship between Co content in sediments and R value

图8 沉积物中钴元素分布特征

Fig.8 Characteristic of Co distribution in sediments

图9 不同地球化学景观区的R值分布 A—岩溶景观区;B—高山峡谷景观区;C—热带雨林景观区;D—半干旱中低山景观区;E—干旱荒漠戈壁残山景观区;F—湿润半湿润高寒山区景观区;G—干旱半干旱高寒山区景观区;H—黄土覆盖景观区;I—湿润半湿润中低山景观区;J—冲积平原景观区;K—森林沼泽景观区。

Fig.9 Distribution of R values of different geochemical landscapes

图10 森林沼泽景观区和湿润半湿润中低山景观区不同Co含量区间R值分布特征

Fig.10 R vaules in geochemical landscapes with different Co content ranges

图11 热带雨林景观区汇水域CGB和RGNR钴含量散点图

Fig.11 Scatter plot of Co contents in catchments by CGB and RGNR in rainforest region

图12 热带雨林景观区海南岛富钴和贫钴源区的差异性剥蚀 a—CGB采样点位与地形和流域的空间关系;b—CGB采样点位与岩性和流域的空间关系; c—汇水域的CGB沉积物钴含量;d—汇水域的RGNR沉积物钴含量。

Fig.12 Differential erosion in Co-rich/poor regions in Hainan of rainforest area

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