Job prospects after completing graduate studies in Geology
Your question has several parts and may be considered too wide for this forum. From what I can see you have a question about your own motivation, which only you can answer. Doing a PhD is a hard job and you need to be motivated to do it successfully. Motivation does not have to be to love your task but also to do it for a goal further on. A PhD is furthermore not just an academic path-breaker. In a PhD are a number of useful skills that are sought after, which include critical thinking, writing, presentation, analysis, synthesis etc.

A second part of your question deals with the job market. To my knowledge geology PhDs do not seem to have problems finding jobs. There is demand for PhD level candidates within both exploration and environmental sectors of industry and government. Being from Sweden, it seems a very high percentage of our students do very well. I do not have any statistics for geology but have numbers for Physical Geography and in that field about 7% had "unknown" jobs whereas the rest had employment in academia, public sector, private sector, NGO, and a small proportion in other fields but all relevant to their education (y-scale is in number of PhDs, QG = Quaternary Geology; PG = Physical Geography):

 

Statistics from the University of Minnesota Geology department shows similar numbers (now, two data points is not much but I think this provides an indication of the value of a PhD in the field of Earth Sciences):



Adding to my second point is a point of social skills. With a higher ranking job, come skills beyond the factual content of an education. I already touched upon the skills but if I look at graduates who really have succeeded, in the sense they left academia and got high-paying and interesting, challenging jobs, most have been able to present themselves very well and this part is not to be understated.

In the end, the possibility of success in job searching after doing a PhD is definitely there but it will without doubt also depend on your own interest in pushing and present yourself and the quality of your work/skills and work ethics.