Although both gold and platinum form placers, they are not found in the same placers because:
a. gold weathers out of felsic rocks, while platinum weathers out of mafic rocks
b. gold weathers out of mafic rocks, while platinum weathers out of felsic rocks
c. gold is soluble under reducing conditions, while platinum is soluble under oxidizing conditions
d. gold is soluble under oxidizing conditions, while platinum is soluble under reducing conditions

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!