中国浙江东部火山岩区成矿作用热流场的计算机仿真/

2019-05-05 05:12:31

仿真 simulation heat ore 成矿



计算机仿真是在计算机上建立仿真模型,模仿实际系统的运行状态及其随时间的变化过程。计算机仿真为一些复杂系统创造了一种计算机实验环境,使系统的性能和长期的动态特性在极短的时间内由计算机得到了全面的实现,是一种有效的实验手段。随着技术的发展,仿真技术的应用在扩大,仿真系统出现多种形式,许多工程与科学技术问题都可以通过仿真求得解决。尤其是近十几年,困扰地质界多年的难题也逐渐通过计算机仿真的方式得以解决,因此计算机仿真技术成为将计算机科学应用于地质学科的重要使用方式。
成矿系列是指在同一地质单元内产出的若干个矿床,它们在成矿时间和成矿过程机理上具有一定的相似性,在矿床成因和控矿地质条件上有某些共性,在矿床的产出和空间分布上具有一定内在联系的一组矿床或矿床组合。火山岩区成矿系列分布的矿床,就其矿种和成因而言,多而复杂。由于成矿演化阶段的不同、成矿具体空间部位的不同、构造和围岩条件的不同,可以形成不同形式的矿床。在浙江省东部火山岩区,成矿系列的空间分带表现出矿种分带和成因分带的双重特点。围绕火山机构中心,矿床将呈由内向外、由深至浅的高温、中温、和低温矿床的分带产出。成因类型则表现出岩浆期后热液型、斑岩型、热液-交代型、火山沉积型以及中间过渡类型等顺次产出的矿床。
通过对浙江东部火山岩区成矿系列的成矿地质背景,控矿条件及成矿规律的详细研究,并从成矿作用流体动力学的角度出发,作者认为在火山岩地区的成矿系列中,成矿时期的热力场热质流动和输运是决定系列中不同矿种矿床形成的最根本因素,热流场的动力学时空演化应该是火山岩区统一成矿作用的具体体现。当岩浆侵入到富含水的多孔介质(围岩)中时,所产生的温度梯度一方面导致热量由岩浆向围岩的热传导和岩浆的冷却,另一方面又导致孔隙溶液产生密度梯度。这两种作用将驱动成矿体系内的热流场发生变化。成矿地质流体在热力的驱动下扩散运移,并在适当部位相继沉淀成矿,最终形成成矿系列。
遵照这一思路,利用计算机仿真技术对浙江东部火山岩地区的热流场进行模拟,首先根据质量守恒原理、能量守恒原理、Darcy定律以及状态方程建立控制方程组,遵从计算机仿真的流程,建立数学模型,仿真模型,编程实现,进行仿真试验,最终仿真结果用Matlab图形功能绘出流线图和温度分布图。
我们假设研究区为充满流体的多孔介质,尽管其内的各个部位可以具有不同的孔隙度和渗透率,但其流体的运动基本属于渗流,满足Darcy定律。数学模型由一组方程(包括守恒方程、运动方程、状态方程)描述,为了方便进行动力学分析和数值运算,对导出的方程组进行了Boussinesq近似和无量纲化。最后得出一个由椭圆方程和抛物方程组成的偏微分方程组。并结合研究区特点和实际情况,建立边界条件和初始条件。
由于相互耦合在一起的偏微分方程组没有解析解,处理难度很大。我们利用有限差分法,对数学模型及边界条件进行离散化数值处理,经过推导得出仿真模型。基于Matlab平台,利用Matlab语言进行编程。最终结果用流线图和温度分布图表示成矿区的热流场(见下图)。为了对仿真模型进行验证和了解动力学参数对仿真结果的影响,在动力学参数合理取值范围内,对渗透率、孔隙度、流体粘度系数进行了仿真试验。系统能够较好的做出反应,证明模型是可以接受的,并且在一定程度上能够反映实际情况。
考虑到岩浆实际侵入的不同情形,将岩浆侵入的形状分成三种情况分别进行模拟,均得到了相同的结果。通过仿真可以得出结论,在浙江东部火山岩发育区,热流场的时空演化在成矿系列的成矿作用过程中具有重要作用,通过热液的循环流动,深部的成矿物质被萃取出来,经过运移并在适当的位置相继沉淀成矿。
本文的创新之处在于:1)首次提出了通过研究成矿系列热流场的方法来研究一组有成因联系的矿床成因机制的思想和方法,通过用计算机仿真的技术手段,来定量刻画和揭示成矿系列形成和分布规律。2)通过详细研究浙江省东部火山岩分布区成矿系列的地质背景、控矿条件、成因机制,全面考虑整个成矿系统的各种影响因素和成矿热质的运动机制,构建了热质流动的定量化模型—热质流动的动力学方程;该模型反映了成矿系列链条中各个独立矿床的联系和控制关系的主要机制和决定性控制因素,对于进一步建立成矿系列定量预测模型来预测和发现成矿链条中尚未发现的可能的漏失矿床或盲矿床具有深远意义。3)利用Matlab数值计算工具箱,编制了热质流动的计算机仿真程序,实现了对成矿系列热流场形成的动态监控。4)首次将计算机仿真技术与成矿系列定量化研究结合起来,对成矿系列形成机制做了有意义的开拓性探讨,对解决我国有关矿产资源紧缺的战略性问题上具有十分现实意义。




Computer simulation builds simulation model on the base of computer and models running state and changes procession of real system along with time. Computer simulation is an effective experimental technique using it creates a kind of computer experimentation environments for complex system, the capacity and long-term dynamic nature of system were comprehensive performed in the short time by the computer. With the development of techniques, the application of simulation is expanding, there appear so many simulation styles, many projects and scientific problems are resolved by simulation. Especially recent years, it resolved many geological difficulties. Therefore, computer simulation will become an important way to apply computer science to geology science.
Metallogenetic series is a series of ore deposits located in the same geological tectonics which have definite comparability in the mineralization time, ore-forming mechanism, some commonness in the cause of metallogenetic and geological conditions of controlling ore deposits, intrinsic relation in the output of the ore deposition and space distribution. The ore deposit distribution of metallogenetic series in the igneous region, as their kinds and the causes of forming, are various and complex. The different type ore deposits were formed in terms of different metallogenetic evolvement phases, different concrete metallogenetic location, different conditions of the tectonic and wall rock. In the igneous region in eastern Zhejiang province, metallogenetic series’ space banding has dual characteristics which are deposition genus banding and forming cause banding. Surrounding the core of the volcanic framework, depositions show high temperature, medium temperature, low temperature banding output from inner to outer and from deep to shallow. The cause type of ore-forming appears hydrothermal after magma type phase, porphyry, hydrothermal-pseudomorphic replacement type, volcanic sedimentary type and intergrade type sequence output.
Through detailed studying of metallogenetic geological background, controlling conditions of deposition and metallogenetic law, from fluid dynamics of ore-forming processes, author thinks the fundamental metallogenetic factor of metallogenetic series in the igneous region is heat-substance flowing and transporting in thermodynamic field in metallogenetic phase, heat-flow field’s dynamic temporal and spatial evolvement should be concrete embodiment of unification ore-forming processes. Magmatic intruding to the porous medium (wall rock)full bearing liquid arose the temperature gradient which induce quantity of heat conduct from magmatic to wall rock and magmatic become cooling, on the other hand, which induce density gradient in the liquid in the medium. The two action change the field of heat flow in the ore-forming system. Metallogenetic geological fluid diffuses and transports with the driving of heat power, sediments one after another in the right location and finally forms the metallogenetic series.
In the light of this idea, we apply computer simulation technique to simulate and modeling the field of the heat flow in the igneous region in eastern Zhejiang province. First of all, constitute the controlling equation sets in terms of the law of mass conservation, the law of energy conservation, and Darcy law. Then following the procedure of computer simulation, it is established the mathematical model and simulation model by coding programs. The third, the simulation experiment is conducted. Finally the simulation results are output with drawing flow line charts and temperature distribution charts by the figure function of the Matlab software.We suppose that the study areas are porous medium full bearing fluid, although there are respective porosities and permeability in different locations, the movement of fluid is seepage basically satisfying Darcy law. Math model was described by a set of equations (including conservation equation, movement equation, state equation). For conveniently dynamic analysis and numerical computing, the sets of equations were concluded with Boussinesq approximation and de-dimension. Finally a set of partial differential equation consists of an ellipse equation set and a parabolic equation set is obtained. Boundary condition and initial condition were constituted according to the peculiarity of study areas and real situation.
It is hard to solve the coupled partial deferential equations because there are no exact resolving methods at present time. We apply the finite differential method to discrete numerical value for mathematical model and boundary conditions, then deducted the computer simulation model. Based on the Matalb platform, the programs were coded with Matlab language. Finally the heat-flow fields in mineralization regions are represented with flow-line charts and temperature distribution charts. In order to verify the simulation model and study the effective of dynamic coefficients to simulation results, the simulation experiment is conducted with various values of permeability, porosity, and viscosity coefficient within reasonable values. The system of heat-flow field is reacted correspondingly to the experiments, and we can conclude that the quantitative model is acceptable and has reflected the real world of the heat-flow fields.
Considering real magnetic intrusions, we simulated three shapes of magnetic intrusions, and the results are same. Through computer simulation, we conclude that heat-flow field played an important role in meineralization of metallogenic series accruing and space evolution in igneous region in eastern Zhejiang province. The basic mechanism of the mineralization of metallogenic series was heat-flowing and circulating with attracting minerals from deep bottom, transporting them to somewhere then minerals were deposited.
The unique aspects of this paper are as follows:
1) A new idea and method regarding discovering mineralization mechanism for a group of ore deposits which are originally related each other has been proposed firstly in this paper. With the proposed method, the forming and distribution regulation of metallogenic series of ore deposits can be quantitatively revealed and described by computer simulation.
2) A quantitative model, a dynamic equation of heat-flow, has been established upon studying the mechanism of heat-flow and various factors of mineralization and analyzing the geological background, the ore-controlling factors, and the mineralization mechanism in igneous region in eastern Zhejiang Province. This model represents key controlling factors and relationship of independent ore deposits in the chain of metallogenic series. This study is significant for further establishing quantitative prediction model of metallogenic series and discovering buried ore deposits.
3) A set of programs of computer simulating heat-flow is developed with Matlab professional tool that can monitor the forming procedure of metallogenic series heat-flow fields.
Combining computer simulation techniques with quantitative study of metallogenic series firstly proposed in this paper that open up a new way and may eventually solve the problem of shortage of mineral resources in China.