Affiliate Marketing Secrets

So here’s the hypothetical case study:
An old woman thinks that her land is rich in gold and can be sold for lots of money. she hires a geologist to check out her land and it turns out that there is no gold, but instead a lot of oil (which she is unaware of). the old woman would like to sell her land for a fair price so she can give the money to her children/grandchildren, but the geologist would like to buy the land from her for cheap so he can let a petroleum company dig oil there (he also has stocks in this company). should the geologist tell the old woman about the oil, or should he keep it a secret then buy the land for way less than it’s actually worth?
So far I thought of:
No – Deontology
deceiving her fails at least two of the three categorical imperatives of Kantianism
Yes – Utilitarianism
he could make more money than the woman, and spend it more wisely/ spend it towards humanitarian efforts instead of letting the old woman’s relatives have it (who knows what they would use it for?)
I also need to bring in a few of: Corporate Social Responsibility, Marketing, Financial, Law, and Environmental Ethics. I feel this is part that I’m having trouble coming up with ideas.