RAW - the spell only damages creatures and creates difficult terrain
In 5e, spells do only what they say they do. In this case, as you say, the spell does damage only to creatures and then makes the area difficult terrain. If the spell was intended to deal damage to objects and terrain it would say so explicitly. In this case "erupting" is just descriptive of the way the dirt and rocks act, but not of any mechanical effects to the surrounding area.
The surface is covered in dirt and rocks, but the spell doesn't say from where
However, the spell never actually says if the churned earth and stone is from the surrounding area at all. As this is a magic spell, it can easily be that these are magically created dirt and rocks. After all, not all "ground" necessarily involves places with dirt and rocks together. The fact that the spell works the same regardless of where you cast it (as long as it is "ground") says that this is probably magically created debris.
Since this is an unclear area of the rules, it is up to the DM to decide how to handle them.
As DM you can tweak the effects to allow creative uses
As a DM you have the latitude to interpret spells to work in different ways than strictly RAW. For example, if this is an area in which ore was prevalent I would probably allow some of that ore to surface as part of the "fountain of churned earth and stone". This is a fun and thematic use of a spell in my opinion, and if you don't have to follow strict RAW then it seems fine to allow it.
Regarding damaging objects with the spell, it makes a bit less sense to me and I am not sure I would allow it. The damage in this case comes from the falling debris not from the "eruption". And I would be careful with ruling to expand the things a spell can affect without careful consideration of other ways it might be used once ruled. There are other spells (eg shatter) that are specifically designed to shatter inorganic objects so I feel like changing this spell to allow that would basically be giving two spells in one. That being said, if you are fine with these objections you can still allow it and see what happens.