成矿元素巨量聚集的混沌机制——斑岩型和构造蚀变岩型矿床例析

Chaotic mechanisms of the ore-forming element accumulation: Case study of porphyry and disseminated-veinlet gold deposits

成矿元素含量的变化受控于成矿系统内部的动力学过程,具有较强的随机性与混沌特征,对其变化特征的定量刻画有助于深入理解成矿过程,并为找矿预测提供理论依据。本文以三江普朗斑岩型铜矿的Cu元素与胶东大尹格庄构造蚀变岩型金矿的Au元素品位序列为研究对象,运用混沌时间序列分析法中的相空间重构技术、吸引子的关联维及最大Lyapunov指数解析了Cu与Au元素品位序列的分布特征。结果显示:斑岩型铜矿强矿化和中矿化Cu元素品位的饱和关联维介于4.42与9.69之间,饱和嵌入维介于25与28之间,最大Lyapunov指数介于0.0021与0.0661之间,弱矿化勘探线Cu元素关联维没有出现饱和现象,最大Lyapunov指数随着嵌入维的增大,由正数变为负数;构造蚀变岩型金矿的强矿化勘探线Au元素的关联维为3.18,饱和嵌入维为23,最大Lyapunov指数为0.0082,而中矿化和弱矿化勘探线Au元素的关联维没有出现饱和现象,且随着嵌入维的增大,最大Lyapunov指数由正数变为负数,表明斑岩型中-强矿化地区的Cu元素和构造蚀变岩型强矿化区域的Au元素品位序列具有混沌动力学特征,而弱矿化地区的Cu元素及中弱矿化地区的Au元素品位序列则具有更强的随机性特征;同时,具有混沌特征的斑岩型铜矿的饱和嵌入维和关联维及最大Lyapunov指数的均值都大于蚀变岩型矿床,说明斑岩型铜矿比蚀变岩型矿床的元素具有更强混沌特性与更复杂的控制因素,如温度、硫化作用、流体不混溶、蚀变叠加等。

The variety of the ore-forming element concentrations,determined by the geodynamic genesis of metallogenic system,bears strongly random and chaos features. Identifying the characteristics of ore-forming elements is significant for better understanding the ore-forming process and mineral prospecting. In this paper,we used the state space reconstruction,correlation dimension of attractor and the maximum Lyapunov exponent from chaotic time series analysis to describe the characteristics of element Cu from Pulang porphyry copper deposit in Sanjiang and element Au from the Dayingezhuang disseminated-veinlet gold deposit in Jiaodong. The results reveal that the ranges of the correlation dimension,embedding dimension and maximum Lyapunov exponent of Cu in intensely and moderately mineralized drill cores are 4. 42 ~ 9. 69,25 ~ 28 and 0. 0021 ~ 0. 0661,separately; whereas the correlation dimensions of Cu in weakly mineralized drill cores are unsaturated. The correlation dimension and the corresponding saturated embedding dimension,and the maximum Lyapunov exponent of Au in intensely mineralized area are 3. 2,23 and 0. 0082,respectively,indicating an obviously chaotic dynamic feature of Au distribution. The correlation dimensions of Au in moderately and weakly mineralized areas are unsaturated,suggesting a strongly random distribution. Furthermore,the means of correlation dimension,embedding dimension and maximum Lyapunov exponent for Cu from porphyry deposit are greater than those for Au from disseminated-veinlet gold deposit,revealing that the ore-forming elements of porphyry deposits have stronger chaotic characteristics,which are considered to subject to the various controls including temperature,sulfidation,fluid immiscibility,and alteration overprinting,etc.