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Q11. Two outcrops on a 1 : 25000 map are 12 cm apart. The ground distance between the two outcrops is ________ km.
The correct answer is 3. The map scale '1 : 25000' means 1 centimeter on the map equals 25,000 centimeters in real life. If the distance is 12 cm on the map, we multiply 12 by 25,000 to get 300,000 centimeters in real life. To convert centimeters to kilometers, we divide by 100,000. 300,000 divided by 100,000 equals exactly 3 kilometers.
Q12. A foliation plane has strike 025o and 60o easterly dip. A mineral lineation on this foliation plane has a rake/pitch of 90o. The plunge direction of the mineral lineation in whole circle bearing is _______degrees.
The correct answer is 115. 'Strike' is the compass direction of the rock layer (25 degrees). 'Dip' is the tilt (easterly). A 'rake' of 90 degrees means the lineation points straight down the steepest part of the tilt (the true dip direction). Since the strike is 025 and it dips east, we add 90 degrees to the strike to find the exact compass direction it is tilting toward. 25 + 90 equals 115 degrees.
Q13. A Cu deposit of 198 tons with average grade of 1.5% Cu contains 60% chalcopyrite, 30% bornite and 10% gangue. The maximum amount of Cu that can be extracted from chalcopyrite is ____________ tons. (Round off to two decimal places)
The total amount of rock dug up is 198 tons, and 1.5% of that is pure copper (about 2.97 tons). This copper comes mixed inside two minerals: chalcopyrite and bornite. Based on their chemical makeup and how much of each mineral is present, the chalcopyrite mineral holds about 1.78 tons of that copper.
Q14. Pumping and extraction of groundwater from an unconfined aquifer resulted in a uniform drop of water table by 40 m over an area of 1 km2. If the porosity of the aquifer is 35% and specific retention is 15%, the volume of water (in m3) pumped out from the affected area is __________ × 10^6 m3. (In integer)
An underground water layer (aquifer) acts like a sponge. When water is pumped out, the water level drops by 40 meters, but some water stays stuck to the rocks (15% retention). The actual water drained is the porosity (35%) minus the stuck water (15%) = 20%. 20% of that massive volume equals 8 million cubic meters of water.
Q15. The cation exchange equilibrium reaction between end-member components of orthopyroxene and ilmenite is given below: MgSiO3 + FeTiO3 = FeSiO3 + MgTiO3. Considering ideal mixing of Fe and Mg in orthopyroxene and ilmenite solid solutions, the mole fractions are XMg Orthopyroxene = 0.60 and XMg Ilmenite = 0.40. The equilibrium constant of the above reaction is ___________. (Round off to two decimal places)
In chemistry, an 'equilibrium constant' is a number that shows how elements balance and trade places between two different minerals when they are heated. Using the given starting amounts (mole fractions) of Iron and Magnesium, the formula calculates this balance point to be around 0.44.
Q16. The apparent dip amount of a limestone bed in the direction 010° is 30°. If the bed strikes 320°, the value of true dip amount in degrees is ___________. (Round off to nearest integer)
'True dip' is the steepest angle a rock layer tilts down into the earth. 'Apparent dip' is the tilt you see if you look at it from a different, non-steepest angle. Using trigonometry on the 30-degree apparent dip and the compass directions, the true steepest tilt calculates to about 37 degrees.
Q17. A Rb–Sr isochron plot of cogenetic volcanic rocks yielded a slope of 0.003. The eruption age of these rocks is __________ Ma. (Round off to one decimal place)
Radiometric dating uses the slow decay of radioactive elements to act as a clock. When plotting the data on a graph (an isochron), the slope of the line reveals the age. By dividing the slope (0.003) by the decay rate of the element Rubidium, scientists calculate the rock erupted about 215.8 million years ago.
Q18. The Throw of a fault is 4 m and the Heave is 3 m. The Dip separation of the fault, in meters, is ____________. (In integer)
When the ground breaks and slips along a slanted fault, it moves diagonally. The vertical drop is the 'Throw' (4 meters) and the horizontal gap is the 'Heave' (3 meters). Using basic geometry (a right triangle), the actual diagonal slip is the square root of (3 squared + 4 squared), which equals 5 meters.
Q19. Consider the present volume of the Earth’s continental crust as 7.5 × 10^18 m3. If continental crust formation started 3.0 Ga ago, then the average rate of continental crustal growth is _________ km3 yr−1. (Round off to one decimal place)
A rate is the total amount divided by the total time. The Earth created 7.5 x 10^18 cubic meters of crust over 3.0 billion years. Dividing the total volume by the time gives exactly 2.5 cubic kilometers of new crust formed every single year.
Q20. A kimberlite pipe has a bulk density of 2.5 g/cc and contains diamond of grade 100 carat/metric ton. If the pipe contains only 1-carat diamond crystals, then the number of diamond crystals per cubic meter in the pipe is _______. (In integer)
A metric ton is 1000 kg. A rock density of 2.5 g/cc means 1 cubic meter of this rock weighs 2500 kg, or 2.5 metric tons. If the rock holds 100 carats of diamond per ton, then 2.5 tons holds 250 carats. Since each diamond is 1 carat, there are 250 diamonds in that cubic meter.