group discussion topic was about global warming and what i feel they were looking for that person should be able to express himself.

Yes there was weighted given to OGPA .

Q:1 Where i did my summer training?
Q:2 What is the system of working there?
Q:3 Level of mechanization in the mine and average productivity of machines?
Q:4 How i can improve the productivity of the mine if i have been appointed the manager of the mine?
Q:4 What is the market price of coal?
Q:5 There were more interrelated questions about geology and mineral?

nopes

do's :
1. Be confident.
2. Be attentive to the manner you are answering.
3. accept if you do not know answer it will save you some time for the questions whose answer you might be knowing.

don'ts:
1.give random answers.
2. Use the technical terms that you do not know much about as it may be as a new question for you.

Selection process: First there was group discussion round and then there was technical and HR interview for candidates selected trough group discussion round.
Out of around 41 mining engineering students who have applied 26 students are finally selected after interview.

I think i was not able to answer them technically sound answers to many of the questions.Luck the most ,good GPA,confidence while facing the questions which i was unable to answer,and answering with positive attitude might have mattered in my favour .