Constraints and Implications of Groundwater Temperature on the Formation of Mississippi Valley-type Zn-Pb Deposits

Martin Appold
,
University of Missouri--Columbia
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Summary

This assignment illustrates the role of groundwater in transporting heat and its implications for the formation of hydrothermal ore deposits. The assignment uses a combination of graphs and algebraic equations that can be readily solved and plotted by hand or using a spreadsheet program. Using relatively simple techniques, key linkages in the sedimentary hydrothermal ore-forming process are demonstrated.

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Context

Audience

The assignment is intended for an undergraduate level course in groundwater hydrology.

Skills and concepts that students must have mastered

To be able to complete this activity, students should already be familiar with flownets and have had an introduction to some basic concepts in heat transport. Familiarity with performing calculations and generating contour (surface) plots in a spreadsheet program like Microsoft Excel will greatly facilitate completion of the assignment. The last question consists of an equilibrium geochemistry calculation and therefore requires some background in this subject.

How the activity is situated in the course

The assignment is intended as a stand-alone problem set to be completed in one week. It is best used toward the end of the course after flow nets, geochemistry, and the role of groundwater in geologic processes have been covered.

Goals

Content/concepts goals for this activity

The assignment is intended to illustrate the role of groundwater in geologic processes, specifically hydrothermal ore formation in sedimentary environments.

Higher order thinking skills goals for this activity

The assignment requires the ability to do spreadsheet programming, to discern cause and effect relationships and the dependence of an outcome on governing input conditions, and to interpret the geologic implications of a computed result.

Other skills goals for this activity

Description of the activity/assignment

This assignment is meant to illustrate how the advection of heat by groundwater leads to the elevated temperatures at shallow sedimentary basin margins at which Mississippi Valley-type Zn-Pb hydrothermal ore deposits are formed. The assignment is based on analytical solutions for groundwater flow and heat transport published by Domenico & Palciauskas (1973). Students use a spreadsheet to calculate and plot the flow field and temperature in a sedimentary basin, and to investigate the conditions needed to produce ore-forming temperatures. These results have further implications for the length of time available for ore formation and the concentration of metals and pH of the groundwater, which are also explored in the assignment. The assignment provides an example of how groundwater plays a fundamental role in an important geologic process in the Earth's crust. The activity also shows the linkages of hydrology to other disciplines such as heat transport, geochemistry, and economic geology.

Determining whether students have met the goals

Students should be able to generate a spreadsheet table of calculations and a contour plot that show temperature, fluid potential, and flow lines over a two-dimensional space. Students should also be able to determine accurately the groundwater velocity, Pb concentration, and pH. Answers to interpretation questions will show whether or not students have properly identified cause and effect relationships in the assignment and their geologic implications.

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