Question

1. You have two schist samples, one containing lots of micas, the other containing lots of micas and garnets. Which of the following statements is true regarding these samples?

a. there is no way to determine which schist sample is higher grade as they are both schist

b. the garnet schist would be considered intrusive (larger grain size) while the mica schist is extrusive (small grain size)

c. the change in metamorphic grade from slate to gneiss is gradational, so within schists there are higher and lower grades - this can be determined based on mineral composition

d. the mica samples is actually phyllite, not schist

2. In the lab activity, you read about the formation of metal sulfide deposits in the Lake Superior Region. Is it possible that metal sulfide deposits are still forming in that region today?

a. yes. but they would be forming quite deep underground and would be not viable for mining

b. no, there deposits formed due to hydrothermal activity before lake superior was present and the water from Lake Superior is too cold to generate more hydrothermal deposits

c. yes, as you move deeper into earth. temperature rises. so the hydrothermal deposits are possible based on Earth's geothermal gradient.

d. no, there are deposits formed during a time of active rifting and associated magmatic activity this is no longer occurring so, a new hydrothermal deposits cannot be formed as the heat source is no longer present.

3. Hydrothermal deposits are mostly associated with:

a. extrusive igneous processes

b. intrusive igneous processes

c. high grade metamorphic processes

d. low grade metamorphic processes

4. as of Oct 2018, new mining permits have been issued to begin a Cu-Ni mining project in the iron range of Minnesota. the mineral formation is associated with the Duluth Complex. The lifetime of the mine is 20 years - after which all of the mineral deposit will have been mined and the mine will be closed. there is rightfully a lot of controversy surrounding this new mining project. Given what you have learned, which of the following are issues that should be considered regarding this mine site?

a. mining impacts water quality (such as acid mine drainage) this will affect the Lake Superior watershed and the boundary water canoe area wilderness

b. creates jobs in an area that relies on mining jobs

c. economic boost from 20 years of mining will be outstripped by the longer lasting economic impact of reduced tourism in an area that will see increased detrimental environmental impacts

d. what is the concentration of the mineral deposit? Is it high enough that even if mineral prices fall, the mine can remain open?

e. mining impacts air quality (dust from mining activity and transportation of mined minerals ) this will affect nearby populated areas.

f. All of these (and many more) are the issues that should be (and have been) considered for this mine site.

Answer 1

1, The change from slate to gneiss is gradational with several different varieties of schist which differs with increasing grade, shown by different mineralogy. So the garnet containing schist is higher grade than the schist containing only mica.

So option c is correct.

2. The metal sulphides deposits are not forming today because active rifting is required to generate the hydrothermal deposits which are not present there today.

So option d is correct.

3. Hydrothermal deposits are mostly associated with intrusive igneous rocks.

So option b is correct.

4. There are many issues that need to be considered for this mine site like acid mine drainage, impact on tourism, economic viability etc.

So option f is correct.